When testing the proposed patch for PR71093 I noticed that it changed the
diagnostic for consteval-prop6.C. I then noticed that the diagnostic wasn't
very helpful either way; it was complaining about modification of the 'x'
variable, but it's not a problem to initialize a local variable with a
consteval constructor as long as the value is actually constant, we want to
know why the value isn't constant. And then it turned out that this also
fixed a missed-optimization bug in the testsuite.
PR c++/108243
gcc/cp/ChangeLog:
* constexpr.cc (cxx_eval_outermost_constant_expr): Turn
a constructor CALL_EXPR into a TARGET_EXPR.