[C++ PATCH] hash-table for extern-c fns.

[C++ PATCH] hash-table for extern-c fns.

https://gcc.gnu.org/ml/gcc-patches/2017-10/msg00614.html
	* name-lookup.c (extern_c_fns): Rename to ...
	(extern_c_decls): ... here.
	(check_extern_c_conflict, extern_c_linkage_bindings): Update.
	(do_pushdecl): Check extern-c fns and vars.

	* g++.dg/lookup/extern-c-redecl6.C: New.
	* g++.dg/lookup/extern-c-hidden.C: Adjust diagnostics.
	* g++.dg/lookup/extern-c-redecl.C: Likewise.
	* g++.old-deja/g++.other/using9.C: Likewise.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@253622 138bc75d-0d04-0410-961f-82ee72b054a4