2017-12-14  Tom de Vries  <tom@codesourcery.com>

	* lib/target-supports.exp (check_effective_target_weak_undefined): New
	proc.
	* gcc.dg/visibility-22.c: Require effective target weak_undefined.

	* doc/sourcebuild.texi (Effective-Target Keywords, Other attributes):
	Add item for weak_undefined.

From-SVN: r255637