testsuite: Add testcase for dangling pointer equality bogus warning [PR104492]

testsuite: Add testcase for dangling pointer equality bogus warning [PR104492]

On Wed, Apr 27, 2022 at 12:02:33PM +0200, Richard Biener wrote:
> I did that but the reduction result did not resemble the same failure
> mode.  I've failed to manually construct a testcase as well.  Possibly
> a testcase using libstdc++ but less Qt internals might be possible.

Here is a testcase that I've managed to reduce, FAILs with:
FAIL: g++.dg/warn/pr104492.C  -std=gnu++14  (test for bogus messages, line 111)
FAIL: g++.dg/warn/pr104492.C  -std=gnu++17  (test for bogus messages, line 111)
FAIL: g++.dg/warn/pr104492.C  -std=gnu++20  (test for bogus messages, line 111)
on both x86_64-linux and i686-linux without your commit and passes with it.

2022-04-27  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/104492
	* g++.dg/warn/pr104492.C: New test.