Add immediate potential_constant_expression variants.
* constexpr.c (potential_constant_expression_1): Add "now" parm.
(is_constant_expression, require_constant_expression): New.
(is_static_init_expression, is_nondependent_constant_expression)
(is_nondependent_static_init_expression): Drop "potential".
* except.c (build_must_not_throw_expr): Do type conversion on
value-dependent argument.
* pt.c, semantics.c, typeck2.c: Use variants without "potential".
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@251423 138bc75d-0d04-0410-961f-82ee72b054a4