re PR tree-optimization/47276 (ICE in function_and_variable_visibility, at ipa.c:857 during compiling glibc.)

	PR tree-optimization/47276 
	* ipa.c (function_and_variable_visibility): Do not try to mark alias
	declarations as needed.
	* gcc.dg/pr47276.c: New testcase.

From-SVN: r168844