build-sys: fix cross-compilation failure caused by building/executing…

… packcc

there exists a ready-to-use macro called `AX_PROG_CXX_FOR_BUILD` which is provided by `ax_prog_cc_for_build.m4` and is widely used for supporting cross-compilation. this macro defined `CC_FOR_BUILD`, `CFLAGS_FOR_BUILD`, `CPPFLAGS_FOR_BUILD`, `LDFLAGS_FOR_BUILD`, `BUILD_EXEEXT` variables. user can set `CC_FOR_BUILD`、`CFLAGS_FOR_BUILD`、`CPPFLAGS_FOR_BUILD`、`LDFLAGS_FOR_BUILD` when cross-compiling. when native-compiling, `FOO_FOR_BUILD` is same as `FOO`. here is a example show you how to use these variables:

configure \
    --host=armv7a-linux-androideabi \
    --prefix=`pwd`/out \
    --enable-static \
    --disable-seccomp \
    CC=/usr/local/opt/android-sdk/ndk-bundle/toolchains/llvm/prebuilt/darwin-x86_64/bin/armv7a-linux-androideabi21-clang \
    CFLAGS='-v' \
    CPP='/usr/local/opt/android-sdk/ndk-bundle/toolchains/llvm/prebuilt/darwin-x86_64/bin/armv7a-linux-androideabi21-clang -E' \
    CPPFLAGS='-I/Users/leleliu008/.ndk-pkg/pkg/jansson/armeabi-v7a/include -I/Users/leleliu008/.ndk-pkg/pkg/libyaml/armeabi-v7a/include -I/Users/leleliu008/.ndk-pkg/pkg/libxml2/armeabi-v7a/include -I/Users/leleliu008/.ndk-pkg/pkg/libiconv/armeabi-v7a/include --sysroot /usr/local/opt/android-sdk/ndk-bundle/toolchains/llvm/prebuilt/darwin-x86_64/sysroot -Qunused-arguments -Dftello=ftell -Dfseeko=fseek' \
    LDFLAGS='-L/Users/leleliu008/.ndk-pkg/pkg/jansson/armeabi-v7a/lib -L/Users/leleliu008/.ndk-pkg/pkg/libyaml/armeabi-v7a/lib -L/Users/leleliu008/.ndk-pkg/pkg/libxml2/armeabi-v7a/lib -L/Users/leleliu008/.ndk-pkg/pkg/libiconv/armeabi-v7a/lib --sysroot /usr/local/opt/android-sdk/ndk-bundle/toolchains/llvm/prebuilt/darwin-x86_64/sysroot' \
    AR=/usr/local/opt/android-sdk/ndk-bundle/toolchains/llvm/prebuilt/darwin-x86_64/bin/arm-linux-androideabi-ar \
    RANLIB=/usr/local/opt/android-sdk/ndk-bundle/toolchains/llvm/prebuilt/darwin-x86_64/bin/arm-linux-androideabi-ranlib \
    CC_FOR_BUILD=/usr/bin/cc \
    CFLAGS_FOR_BUILD='-v' \
    PKG_CONFIG_PATH=/Users/leleliu008/.ndk-pkg/pkg/libiconv/armeabi-v7a/lib/pkgconfig:/Users/leleliu008/.ndk-pkg/pkg/libxml2/armeabi-v7a/lib/pkgconfig:/Users/leleliu008/.ndk-pkg/pkg/libyaml/armeabi-v7a/lib/pkgconfig:/Users/leleliu008/.ndk-pkg/pkg/jansson/armeabi-v7a/lib/pkgconfig \
    PKG_CONFIG_LIBDIR=/Users/leleliu008/.ndk-pkg/pkg

ax_prog_cc_for_build.m4 has been downloaded from `http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=blob_plain;f=m4/ax_prog_cc_for_build.m4` and placed in m4 directory. to use aclocal from Automake to generate aclocal.m4, we must also set `ACLOCAL_AMFLAGS = -I m4` in top-level Makefile.am.

build packcc don't follow `The Uniform Naming Scheme`. because automake auto append `$(EXEEXT)` to `*_PROGRAMS` when generating the Makefile, but here we want to use `$(BUILD_EXEEXT)`. as we don't use `The Uniform Naming Scheme`, we must clean `packcc` and `packcc.exe` by myself.

References:
*https://www.gnu.org/software/autoconf-archive/ax_prog_cc_for_build.html
*https://www.gnu.org/software/autoconf/manual/autoconf-2.69/html_node/Input.html
*https://www.gnu.org/software/automake/manual/html_node/Uniform.html

Makefile.am

@@ -1,3 +1,5 @@
+ACLOCAL_AMFLAGS = -I m4
+
 include $(top_srcdir)/source.mak
 
 EXTRA_DIST   = README.md autogen.sh \
@@ -9,7 +11,7 @@ EXTRA_DIST   = README.md autogen.sh \
 	       misc/ctags-optlib-mode.el \
 	       misc/mk-interactive-request.sh misc/roundtrip misc/tinst \
 	       misc/packcc/.gitignore misc/packcc/LICENSE.txt \
-	       misc/packcc/README.md \
+	       misc/packcc/README.md misc/packcc/packcc.c \
 	       misc/validators/validator-jq \
 	       misc/validators/validator-KNOWN-INVALIDATION \
 	       misc/validators/validator-NONE \
@@ -28,6 +30,7 @@ CLEANFILES =
 MOSTLYCLEANFILES =
 
 clean-local:
+	rm -f packcc$(BUILD_EXEEXT)
 	@if test "$(top_srcdir)" != "$(top_builddir)"; then \
 		rm -rf $(OPTLIB2C_SRCS); \
 	fi
@@ -36,18 +39,16 @@ bin_PROGRAMS = ctags
 noinst_LIBRARIES = libctags.a
 
 noinst_PROGRAMS =
-noinst_PROGRAMS += packcc
 noinst_PROGRAMS += mini-geany
 
-packcc_CPPFLAGS =
-packcc_CFLAGS  =
-packcc_CFLAGS += $(EXTRA_CFLAGS)
-dist_packcc_SOURCES = $(PACKCC_SRCS)
-
-if HAVE_STRNLEN
-packcc_CPPFLAGS += -DUSE_SYSTEM_STRNLEN
+if HAVE_STRNLEN_FOR_BUILD
+EXTRA_CPPFLAGS_FOR_BUILD = -DUSE_SYSTEM_STRNLEN
 endif
 
+PACKCC = $(top_builddir)/packcc$(BUILD_EXEEXT)
+
+$(PACKCC):
+	$(CC_FOR_BUILD) $(CFLAGS_FOR_BUILD) $(CPPFLAGS_FOR_BUILD) $(EXTRA_CPPFLAGS_FOR_BUILD) $(LDFLAGS_FOR_BUILD) -o $@ $(top_srcdir)/misc/packcc/packcc.c
 
 if USE_READCMD
 bin_PROGRAMS+= readtags
@@ -143,14 +144,13 @@ endif
 packcc_verbose = $(packcc_verbose_@AM_V@)
 packcc_verbose_ = $(packcc_verbose_@AM_DEFAULT_V@)
 packcc_verbose_0 = @echo PACKCC "    $@";
-PACKCC = $(top_builddir)/packcc$(EXEEXT)
 SUFFIXES += .peg
 .peg.c:
 	$(packcc_verbose)$(PACKCC) -i \"general.h\" -o $(top_builddir)/peg/$(*F) "$<"
 .peg.h:
 	$(packcc_verbose)$(PACKCC) -i \"general.h\" -o $(top_builddir)/peg/$(*F) "$<"
 # You cannot use $(PACKCC) as a target name here.
-$(PEG_SRCS) $(PEG_HEADS): packcc$(EXEEXT) Makefile
+$(PEG_SRCS) $(PEG_HEADS): $(PACKCC) Makefile
 dist_libctags_a_SOURCES = $(ALL_LIB_HEADS) $(ALL_LIB_SRCS)
 
 ctags_CPPFLAGS = $(libctags_a_CPPFLAGS)

configure.ac

@@ -28,6 +28,7 @@ uname -mrsv 2>/dev/null
 AM_INIT_AUTOMAKE([foreign subdir-objects tar-ustar])
 AM_SILENT_RULES([yes])
 AC_CONFIG_HEADERS([config.h])
+AC_CONFIG_MACRO_DIR([m4])
 
 AC_CANONICAL_BUILD
 AC_CANONICAL_HOST
@@ -240,6 +241,25 @@ AC_PROG_CC_C99
 AC_PROG_RANLIB
 AC_C_BIGENDIAN
 
+# https://www.gnu.org/software/autoconf-archive/ax_prog_cc_for_build.html
+AX_PROG_CC_FOR_BUILD
+
+# We need to compile and run a program on the build machine.
+AC_MSG_CHECKING(for cc for build)
+if test "$cross_compiling" = "yes"; then
+  CC_FOR_BUILD="${CC_FOR_BUILD-cc}"
+else
+  CC_FOR_BUILD="${CC_FOR_BUILD-$CC}"
+  CFLAGS_FOR_BUILD="${CFLAGS_FOR_BUILD-$CFLAGS}"
+  CPPFLAGS_FOR_BUILD="${CPPFLAGS_FOR_BUILD-$CPPFLAGS}"
+  LDFLAGS_FOR_BUILD="${LDFLAGS_FOR_BUILD-$LDFLAGS}"
+fi
+AC_MSG_RESULT($CC_FOR_BUILD)
+AC_ARG_VAR(CC_FOR_BUILD,[build system C compiler])
+AC_ARG_VAR(CFLAGS_FOR_BUILD,[CFLAGS for build system C compiler])
+AC_ARG_VAR(CPPFLAGS_FOR_BUILD,[CPPFLAGS for build system C compiler])
+AC_ARG_VAR(LDFLAGS_FOR_BUILD,[LDFLAGS for build system C compiler])
+
 if test "${with_sparse_cgcc}" = "yes"; then
 	REAL_CC="${CC}"
 	CC="cgcc"
@@ -706,6 +726,21 @@ AC_CHECK_DECLS([strnlen],[have_strnlen=yes],[],[
 ])
 AM_CONDITIONAL(HAVE_STRNLEN, test "x$have_strnlen" = xyes)
 
+AC_MSG_CHECKING(whether strnlen is declared for build)
+TEMP_DIR_FOR_CHECKING=$(mktemp -d || exit 1)
+cat > "$TEMP_DIR_FOR_CHECKING/test.c" <<EOF
+#include<string.h>
+int main() { strnlen("abcd",1); return 0;}
+EOF
+
+if $CC_FOR_BUILD $CPPFLAGS_FOR_BUILD $CFLAGS_FOR_BUILD -o "$TEMP_DIR_FOR_CHECKING/test.o" "$TEMP_DIR_FOR_CHECKING/test.c" > /dev/null 2>&1 ; then
+    have_strnlen_for_build=yes
+else
+    have_strnlen_for_build=no
+fi
+AC_MSG_RESULT($have_strnlen_for_build)
+AM_CONDITIONAL(HAVE_STRNLEN_FOR_BUILD, test "x$have_strnlen_for_build" = xyes)
+
 if test "$CTAGS_NAME_EXECUTABLE" != ctags ; then
 	AC_MSG_NOTICE(Changing name of 'ctags' for $CTAGS_NAME_EXECUTABLE)
 fi

m4/ax_prog_cc_for_build.m4

@@ -0,0 +1,139 @@
+# ===========================================================================
+#   https://www.gnu.org/software/autoconf-archive/ax_prog_cc_for_build.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_PROG_CC_FOR_BUILD
+#
+# DESCRIPTION
+#
+#   This macro searches for a C compiler that generates native executables,
+#   that is a C compiler that surely is not a cross-compiler. This can be
+#   useful if you have to generate source code at compile-time like for
+#   example GCC does.
+#
+#   The macro sets the CC_FOR_BUILD and CPP_FOR_BUILD macros to anything
+#   needed to compile or link (CC_FOR_BUILD) and preprocess (CPP_FOR_BUILD).
+#   The value of these variables can be overridden by the user by specifying
+#   a compiler with an environment variable (like you do for standard CC).
+#
+#   It also sets BUILD_EXEEXT and BUILD_OBJEXT to the executable and object
+#   file extensions for the build platform, and GCC_FOR_BUILD to `yes' if
+#   the compiler we found is GCC. All these variables but GCC_FOR_BUILD are
+#   substituted in the Makefile.
+#
+# LICENSE
+#
+#   Copyright (c) 2008 Paolo Bonzini <bonzini@gnu.org>
+#
+#   Copying and distribution of this file, with or without modification, are
+#   permitted in any medium without royalty provided the copyright notice
+#   and this notice are preserved. This file is offered as-is, without any
+#   warranty.
+
+#serial 18
+
+AU_ALIAS([AC_PROG_CC_FOR_BUILD], [AX_PROG_CC_FOR_BUILD])
+AC_DEFUN([AX_PROG_CC_FOR_BUILD], [dnl
+AC_REQUIRE([AC_PROG_CC])dnl
+AC_REQUIRE([AC_PROG_CPP])dnl
+AC_REQUIRE([AC_CANONICAL_BUILD])dnl
+
+dnl Use the standard macros, but make them use other variable names
+dnl
+pushdef([ac_cv_prog_CPP], ac_cv_build_prog_CPP)dnl
+pushdef([ac_cv_prog_cc_c89], ac_cv_build_prog_cc_c89)dnl
+pushdef([ac_cv_prog_gcc], ac_cv_build_prog_gcc)dnl
+pushdef([ac_cv_prog_cc_works], ac_cv_build_prog_cc_works)dnl
+pushdef([ac_cv_prog_cc_cross], ac_cv_build_prog_cc_cross)dnl
+pushdef([ac_cv_prog_cc_g], ac_cv_build_prog_cc_g)dnl
+pushdef([ac_cv_c_compiler_gnu], ac_cv_build_c_compiler_gnu)dnl
+pushdef([ac_cv_exeext], ac_cv_build_exeext)dnl
+pushdef([ac_cv_objext], ac_cv_build_objext)dnl
+pushdef([ac_exeext], ac_build_exeext)dnl
+pushdef([ac_objext], ac_build_objext)dnl
+pushdef([CC], CC_FOR_BUILD)dnl
+pushdef([CPP], CPP_FOR_BUILD)dnl
+pushdef([GCC], GCC_FOR_BUILD)dnl
+pushdef([CFLAGS], CFLAGS_FOR_BUILD)dnl
+pushdef([CPPFLAGS], CPPFLAGS_FOR_BUILD)dnl
+pushdef([EXEEXT], BUILD_EXEEXT)dnl
+pushdef([LDFLAGS], LDFLAGS_FOR_BUILD)dnl
+pushdef([OBJEXT], BUILD_OBJEXT)dnl
+pushdef([host], build)dnl
+pushdef([host_alias], build_alias)dnl
+pushdef([host_cpu], build_cpu)dnl
+pushdef([host_vendor], build_vendor)dnl
+pushdef([host_os], build_os)dnl
+pushdef([ac_cv_host], ac_cv_build)dnl
+pushdef([ac_cv_host_alias], ac_cv_build_alias)dnl
+pushdef([ac_cv_host_cpu], ac_cv_build_cpu)dnl
+pushdef([ac_cv_host_vendor], ac_cv_build_vendor)dnl
+pushdef([ac_cv_host_os], ac_cv_build_os)dnl
+pushdef([ac_tool_prefix], ac_build_tool_prefix)dnl
+pushdef([am_cv_CC_dependencies_compiler_type], am_cv_build_CC_dependencies_compiler_type)dnl
+pushdef([am_cv_prog_cc_c_o], am_cv_build_prog_cc_c_o)dnl
+pushdef([cross_compiling], cross_compiling_build)dnl
+
+cross_compiling_build=no
+
+ac_build_tool_prefix=
+AS_IF([test -n "$build"],      [ac_build_tool_prefix="$build-"],
+      [test -n "$build_alias"],[ac_build_tool_prefix="$build_alias-"])
+
+AC_LANG_PUSH([C])
+AC_PROG_CC
+_AC_COMPILER_EXEEXT
+_AC_COMPILER_OBJEXT
+AC_PROG_CPP
+
+dnl Restore the old definitions
+dnl
+popdef([cross_compiling])dnl
+popdef([am_cv_prog_cc_c_o])dnl
+popdef([am_cv_CC_dependencies_compiler_type])dnl
+popdef([ac_tool_prefix])dnl
+popdef([ac_cv_host_os])dnl
+popdef([ac_cv_host_vendor])dnl
+popdef([ac_cv_host_cpu])dnl
+popdef([ac_cv_host_alias])dnl
+popdef([ac_cv_host])dnl
+popdef([host_os])dnl
+popdef([host_vendor])dnl
+popdef([host_cpu])dnl
+popdef([host_alias])dnl
+popdef([host])dnl
+popdef([OBJEXT])dnl
+popdef([LDFLAGS])dnl
+popdef([EXEEXT])dnl
+popdef([CPPFLAGS])dnl
+popdef([CFLAGS])dnl
+popdef([GCC])dnl
+popdef([CPP])dnl
+popdef([CC])dnl
+popdef([ac_objext])dnl
+popdef([ac_exeext])dnl
+popdef([ac_cv_objext])dnl
+popdef([ac_cv_exeext])dnl
+popdef([ac_cv_c_compiler_gnu])dnl
+popdef([ac_cv_prog_cc_g])dnl
+popdef([ac_cv_prog_cc_cross])dnl
+popdef([ac_cv_prog_cc_works])dnl
+popdef([ac_cv_prog_cc_c89])dnl
+popdef([ac_cv_prog_gcc])dnl
+popdef([ac_cv_prog_CPP])dnl
+
+dnl restore global variables ac_ext, ac_cpp, ac_compile,
+dnl ac_link, ac_compiler_gnu (dependant on the current
+dnl language after popping):
+AC_LANG_POP([C])
+
+dnl Finally, set Makefile variables
+dnl
+AC_SUBST(BUILD_EXEEXT)dnl
+AC_SUBST(BUILD_OBJEXT)dnl
+AC_SUBST([CFLAGS_FOR_BUILD])dnl
+AC_SUBST([CPPFLAGS_FOR_BUILD])dnl
+AC_SUBST([LDFLAGS_FOR_BUILD])dnl
+])