testsuite: Expect -Wdeprecated warning in warn/Wstrict-aliasing-bogus-union-2.C for C++23

On Mon, Feb 06, 2023 at 02:26:01PM +0000, Jonathan Wakely via Gcc-patches wrote:
> With the recent change to deprecate std::aligned_storage and
> std::aligned_union we need to adjust some tests that now fail with
> -std=c++23.

The g++.dg/warn/Wstrict-aliasing-bogus-union-2.C test is also affected:
PASS: g++.dg/warn/Wstrict-aliasing-bogus-union-2.C  -std=gnu++2b  (test for bogus messages, line 12)
FAIL: g++.dg/warn/Wstrict-aliasing-bogus-union-2.C  -std=gnu++2b (test for excess errors)
Excess errors:
.../gcc/testsuite/g++.dg/warn/Wstrict-aliasing-bogus-union-2.C:8:8: warning: 'template<long unsigned int _Len, long unsigned int _Align> struct std::aligned_storage' is deprecated [-

The following patch adds dg-warning for it.

2023-02-07  Jakub Jelinek  <jakub@redhat.com>

	* g++.dg/warn/Wstrict-aliasing-bogus-union-2.C: Expect
	-Wdeprecated warning for C++23.