PR c/18946
	* c-decl.c (warn_if_shadowing): Handle old_decl error_mark_node.
	(pushdecl): Only use DECL_FILE_SCOPE_P if DECL_P.
	(implicitly_declare): Handle error_mark_node.

	* gcc.dg/noncompile/20050120-1.c: New test.

From-SVN: r94320