PR c++/91346 - Implement P1668R1, allow unevaluated asm in constexpr.

PR c++/91346 - Implement P1668R1, allow unevaluated asm in constexpr.

	* constexpr.c (cxx_eval_constant_expression): Handle ASM_EXPR.
	(potential_constant_expression_1) <case ASM_EXPR>: Allow.
	* cp-tree.h (finish_asm_stmt): Adjust.
	* parser.c (cp_parser_asm_definition): Grab the locaion of "asm" and
	use it.  Change an error to a pedwarn.  Allow asm in C++2a, warn
	otherwise.
	* pt.c (tsubst_expr): Pass a location down to finish_asm_stmt.
	* semantics.c (finish_asm_stmt): New location_t parameter.  Use it.

	* g++.dg/cpp2a/inline-asm1.C: New test.
	* g++.dg/cpp2a/inline-asm2.C: New test.
	* g++.dg/cpp1y/constexpr-neg1.C: Adjust dg-error.

From-SVN: r274169