Handle PHI nodes w/o a argument (PR ipa/80205).

2017-03-28  Martin Liska  <mliska@suse.cz>

	PR ipa/80205
	* g++.dg/ipa/pr80205.C: New test.
2017-03-28  Richard Biener  <rguenther@suse.de>

	PR ipa/80205
	* tree-inline.c (copy_phis_for_bb): Do not create PHI node
	without arguments, generate default definition of a SSA name.

From-SVN: r246530