build: Integrate venvlauncher build/installation into the Makefile

This is required for venv creation on Windows.
Ideally this would use the venv specific launcher (PC/launcher.c),
but a copy of main binary seems to work as well for now.

Makefile.pre.in

@@ -167,6 +167,7 @@ BINLIBDEST=	@BINLIBDEST@
 LIBDEST=	$(SCRIPTDIR)/python$(VERSION)
 INCLUDEPY=	$(INCLUDEDIR)/python$(LDVERSION)
 CONFINCLUDEPY=	$(CONFINCLUDEDIR)/python$(LDVERSION)
+VENVLAUNCHERDIR=	$(BINLIBDEST)/venv/scripts/nt
 
 # Symbols used for using shared libraries
 SHLIB_SUFFIX=	@SHLIB_SUFFIX@
@@ -295,6 +296,8 @@ LIBOBJS=	@LIBOBJS@
 PYTHON=		python$(EXE)
 BUILDPYTHON=	python$(BUILDEXE)
 BUILDPYTHONW=	pythonw$(BUILDEXE)
+BUILDVENVLAUNCHER=	venvlauncher$(BUILDEXE)
+BUILDVENVWLAUNCHER=	venvwlauncher$(BUILDEXE)
 
 HOSTRUNNER= @HOSTRUNNER@
 
@@ -597,7 +600,7 @@ LIBEXPAT_HEADERS= \
 
 # Default target
 all:		@DEF_MAKE_ALL_RULE@
-build_all:	check-clean-src $(BUILDPYTHON) $(BUILDPYTHONW) platform oldsharedmods sharedmods \
+build_all:	check-clean-src $(BUILDPYTHON) $(BUILDPYTHONW) $(BUILDVENVLAUNCHER) $(BUILDVENVWLAUNCHER) platform oldsharedmods sharedmods \
 		gdbhooks Programs/_testembed python-config
 build_wasm: check-clean-src $(BUILDPYTHON) platform oldsharedmods python-config
 
@@ -729,6 +732,14 @@ $(BUILDPYTHONW): Programs/python.o $(LIBRARY) $(LDLIBRARY) $(PY3LIBRARY) pythonw
 $(BUILDPYTHON):	Programs/python.o $(LINK_PYTHON_DEPS) python_exe.o
 	$(LINKCC) $(PY_CORE_LDFLAGS) $(LINKFORSHARED) -municode -o $@ Programs/python.o $(LINK_PYTHON_OBJS) $(LIBS) $(MODLIBS) $(SYSLIBS) python_exe.o
 
+# FIXME: build these from PC/launcher.c instead
+$(BUILDVENVLAUNCHER): $(BUILDPYTHON)
+	cp $(BUILDPYTHON) $(BUILDVENVLAUNCHER)
+
+# FIXME: build these from PC/launcher.c instead
+$(BUILDVENVWLAUNCHER): $(BUILDPYTHONW)
+	cp $(BUILDPYTHONW) $(BUILDVENVWLAUNCHER)
+
 platform: $(PYTHON_FOR_BUILD_DEPS) pybuilddir.txt
 	$(RUNSHARED) $(PYTHON_FOR_BUILD) -c 'import sys ; from sysconfig import get_platform ; print("%s-%d.%d" % (get_platform(), *sys.version_info[:2]))' >platform
 
@@ -1821,7 +1832,7 @@ $(DESTSHARED):
 # Install the interpreter with $(VERSION) affixed
 # This goes into $(exec_prefix)
 altbininstall: $(BUILDPYTHON) @FRAMEWORKPYTHONW@
-	@for i in $(BINDIR) $(LIBDIR); \
+	@for i in $(BINDIR) $(LIBDIR) $(VENVLAUNCHERDIR); \
 	do \
 		if test ! -d $(DESTDIR)$$i; then \
 			echo "Creating directory $$i"; \
@@ -1832,6 +1843,8 @@ altbininstall: $(BUILDPYTHON) @FRAMEWORKPYTHONW@
 	if test "$(PYTHONFRAMEWORKDIR)" = "no-framework" ; then \
 		$(INSTALL_PROGRAM) $(BUILDPYTHON) $(DESTDIR)$(BINDIR)/python$(LDVERSION)$(EXE); \
 		$(INSTALL_PROGRAM) $(BUILDPYTHONW) $(DESTDIR)$(BINDIR)/python3w$(EXE); \
+		$(INSTALL_PROGRAM) $(BUILDPYTHON) $(DESTDIR)$(VENVLAUNCHERDIR)/python$(EXE); \
+		$(INSTALL_PROGRAM) $(BUILDPYTHONW) $(DESTDIR)$(VENVLAUNCHERDIR)/pythonw$(EXE); \
 	else \
 		$(INSTALL_PROGRAM) $(STRIPFLAG) Mac/pythonw $(DESTDIR)$(BINDIR)/python$(LDVERSION)$(EXE); \
 	fi