[PR85569] skip constexpr target_expr constructor dummy type conversion

[PR85569] skip constexpr target_expr constructor dummy type conversion

The testcase is the work-around testcase for the PR; even that had
started failing.  The problem was that, when unqualifying the type of
a TARGET_EXPR, we'd create a variant of the type, then request the
conversion of the TARGET_EXPR_INITIAL to that variant type.  Though
the types are different pointer-wise, they're the same_type_p, so the
resulting modified expr compares cp_tree_equal to the original, which
maybe_constant_value flags as an error.  There's no reason to
construct an alternate TARGET_EXPR or CONSTRUCTOR just because of an
equivalent type, except for another spot that expected pointer
equality that would no longer be satisfied.  Without relaxing the
assert in constexpr_call_hasher::equal, g++.robertl/eb73.C would
trigger an assertion failure.

for  gcc/cp/ChangeLog

	PR c++/85569
	* constexpr.c (adjust_temp_type): Test for type equality with
	same_type_p.
	(constexpr_call_hasher::equal): Likewise.

for  gcc/testsuite/ChangeLog

	PR c++/85569
	* g++.dg/cpp1z/pr85569.C: New.

From-SVN: r266816