Wrappers for lookup_qualified_name and build_x_binary_op to make calling
them more convenient in places, and a function named contextual_conv_bool
for places that want contextual conversion to bool.

I noticed that we weren't showing the declaration location when we complain
about a call to a non-constexpr function where a constant expression is
required.

If maybe_instantiate_noexcept doesn't actually instantiate, there's no
reason for it to mess with clones.

	* constexpr.c (explain_invalid_constexpr_fn): Show location of fn.

	* pt.c (maybe_instantiate_noexcept): Only update clones if we
	instantiated.

	* typeck.c (contextual_conv_bool): New.

	* name-lookup.c (lookup_qualified_name): Add wrapper overload taking
	C string rather than identifier.
	* parser.c (cp_parser_userdef_numeric_literal): Use it.
	* rtti.c (emit_support_tinfos): Use it.
	* cp-tree.h (ovl_op_identifier): Change to inline functions.
	(build_x_binary_op): Add wrapper with fewer parms.

From-SVN: r277862