PR bootstrap/50777
	* configure.ac: Save and restore CXXFLAGS around
	gcc_AC_CHECK_DECLS uses.
	Check for madvise() declaration with g++ if --enable-build-with-cxx.
	* configure: Regenerate.
	* config.in: Regenerate.
	* ggc-page.c (USING_MADVISE): Also check HAVE_DECL_MADVISE.

From-SVN: r180195