testsuite: Add testcase for already fixed PR [PR100469]

This bug introduced in r11-7448-gff92ede8d269375f800e1b347a48f4698874b4a3
has been fixed already by r12-1354-g2d2ed777b23ab6503027039e0adbfe1162f52b2f
aka PR100852 fix.

2021-11-15  Jakub Jelinek  <jakub@redhat.com>

	PR debug/100469
	* g++.dg/opt/pr100469.C: New test.