Add defs for makefile installation dir vars

Add macro definitions to AM_CPPFLAGS to propagate makefile installation
directory variables for libexecdir, runstatedir, sbindir, and
sysconfdir.

https://www.gnu.org/software/autoconf/manual/autoconf-2.69/html_node/Installation-Directory-Variables.html

  A corollary is that you should not use these variables except
  in makefiles. For instance, instead of trying to evaluate
  datadir in configure and hard-coding it in makefiles using e.g.,
  'AC_DEFINE_UNQUOTED([DATADIR], ["$datadir"], [Data directory.])',
  you should add -DDATADIR='$(datadir)' to your makefile's definition
  of CPPFLAGS (AM_CPPFLAGS if you are also using Automake).

The runstatedir directory is for "installing data files which the
programs modify while they run, that pertain to one specific machine,
and which need not persist longer than the execution of the program".

https://www.gnu.org/prep/standards/html_node/Directory-Variables.html

It will be defined by autoconf 2.70 or later, and default to
"$(localstatedir)/run".

http://git.savannah.gnu.org/gitweb/?p=autoconf.git;a=commit;h=a197431414088a417b407b9b20583b2e8f7363bd

Signed-off-by: Chris Dunlap <cdunlap@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #2

config/Rules.am

@@ -8,3 +8,7 @@ AM_CFLAGS += -fno-strict-aliasing
 AM_CPPFLAGS  = -D_GNU_SOURCE -D__EXTENSIONS__ -D_REENTRANT
 AM_CPPFLAGS += -D_POSIX_PTHREAD_SEMANTICS -D_FILE_OFFSET_BITS=64
 AM_CPPFLAGS += -D_LARGEFILE64_SOURCE -DTEXT_DOMAIN=\"zfs-linux-user\"
+AM_CPPFLAGS += -DLIBEXECDIR=\"$(libexecdir)\"
+AM_CPPFLAGS += -DRUNSTATEDIR=\"$(runstatedir)\"
+AM_CPPFLAGS += -DSBINDIR=\"$(sbindir)\"
+AM_CPPFLAGS += -DSYSCONFDIR=\"$(sysconfdir)\"

config/user-runstatedir.m4

@@ -0,0 +1,6 @@
+dnl For backwards compatibility; runstatedir added in autoconf 2.70.
+AC_DEFUN([ZFS_AC_CONFIG_USER_RUNSTATEDIR], [
+	if test "x$runstatedir" = x; then
+		AC_SUBST([runstatedir], ['${localstatedir}/run'])
+	fi
+])

config/user.m4

@@ -12,4 +12,5 @@ AC_DEFUN([ZFS_AC_CONFIG_USER], [
 	ZFS_AC_CONFIG_USER_LIBUUID
 	ZFS_AC_CONFIG_USER_LIBBLKID
 	ZFS_AC_CONFIG_USER_FRAME_LARGER_THAN
+	ZFS_AC_CONFIG_USER_RUNSTATEDIR
 ])