[C++ PATCH] Deprecate -ffriend-injection

[C++ PATCH] Deprecate -ffriend-injection

https://gcc.gnu.org/ml/gcc-patches/2018-02/msg00998.html
	Deprecate -ffriend-injection.
	* decl.c (cxx_init_decl_processing): Emit warning on option.
	* name-lookup.c (do_pushdecl): Emit warning if we push a visible
	friend.

	* doc/extend.texi (Backwards Compatibility): Mention friend
	injection.  Note for-scope is deprecated.
	* doc/invoke.texi (-ffriend-injection): Deprecate.

	* g++.old-deja/g++.jason/scoping15.C: Expect warnings.
	* g++.old-deja/g++.mike/net43.C: Likewise.

From-SVN: r257742