re PR middle-end/46949 (ICE when weakref is used on a definition (internal compiler error: in function_and_variable_visibility, at ipa.c:904))

	PR middle-end/46949
	* cgraphunit.c (process_common_attributes): Fix use of remove_attribute.
	(process_function_and_variable_attributes): Check defined weakrefs.
	* gcc.dg/attr-weakref-4.c: New testcase

From-SVN: r169332