c: Fix ICE for redeclaration of structs with different alignment [PR114727]

c: Fix ICE for redeclaration of structs with different alignment [PR114727]

For redeclarations of struct in C23, if one has an alignment attribute
that makes the alignment different, we later get an ICE in verify_types.
This patches disallows such redeclarations by declaring such types to
be different.

	PR c/114727

gcc/c/
	* c-typeck.cc (tagged_types_tu_compatible): Add test.

gcc/testsuite/
	* gcc.dg/pr114727.c: New test.