* cppinit.c (remove_dup_dirs): Inform if a system include
        directory is being reordered.
	* doc/invoke.texi (Directory Options): GCC warns if you hide a
	system include.
	* doc/cpp.texi (Search Paths): Likewise.
	* doc/gcc.texi (Interoperation): Remove information about
	-I/usr/include.

From-SVN: r43769