c-decl.c (diagnose_mismatched_decls): Give error for external redeclaration of identifier declared with no linkage...

	* c-decl.c (diagnose_mismatched_decls): Give error for external
	redeclaration of identifier declared with no linkage, not just
	warning with -Wtraditional.  Do not check DECL_CONTEXT to give
	error for redeclaration with no linkage.

testsuite:
	* gcc.dg/redecl-2.c: New test.

From-SVN: r85386