c++: Avoid concept evaluation when uid-sensitive [PR94038]

Concept evaluation may entail DECL_UID generation and/or template
instantiation, so in general we can't perform it during uid-sensitive
constexpr evaluation.

gcc/cp/ChangeLog:

	PR c++/94038
	* constexpr.c (cxx_eval_constant_expression)
	<case TEMPLATE_ID_EXPR>: Don't evaluate the concept when
	constexpr evaluation is uid-sensitive.

gcc/testsuite/ChangeLog:

	PR c++/94038
	* g++.dg/warn/pr94038-3.C: New test.