* c-common.c (shadow_warning): New function, moved from cp/decl.c.
	* c-common.h (shadow_warning): New.
	* c-decl.c: Include c-common.h.
	(warn_if_shadowing): New, broken out of pushdecl.
	(pushdecl): Use warn_if_shadowing.
	(store_parm_decls): Prevent duplicate -Wshadow warnings.
cp:
	* decl.c: Include c-common.h.
	(shadow_warning): Move to c-common.c.
testsuite:
	* gcc.dg/Wshadow-1.c: New test.

From-SVN: r47701