configure.in: For *-*-cygwin32*, add a -I for winsup to both XCINCLUDES and XCXXINCLUDES.

	* configure.in: For *-*-cygwin32*, add a -I for winsup to both
	XCINCLUDES and XCXXINCLUDES.
	* config.shared: Use ${host_includes} when setting CXXINCLUDES in
	the DOING_LIBGXX case.
	* Makefile.in (_G_config.h): Pass $(CINCLUDES) in CC and
	$(CXXINCLUDES) in CXX when running gen-params.
	* config.shared (THIS_FILE): Really found via TOLIBIO instead
	of TOLIBCXX, which is empty when configuring gperf.
	(LIBS): When linking gperf, find libstdc++ relative to TO_TOPDIR
	instead of hardcoded "../".

From-SVN: r18168