c++: Reject UDLs in certain contexts [PR105300]

c++: Reject UDLs in certain contexts [PR105300]

In this PR, we are crashing because we've encountered a UDL where a
string-literal is expected.  This patch makes the parser reject string
and character UDLs in all places where the grammar requires a
string-literal and not a user-defined-string-literal.

I've introduced two new wrappers; the existing cp_parser_string_literal
was renamed to cp_parser_string_literal_common and should not be called
directly.  finish_userdef_string_literal is renamed from
cp_parser_userdef_string_literal.

	PR c++/105300

gcc/c-family/ChangeLog:

	* c-pragma.cc (handle_pragma_message): Warn for CPP_STRING_USERDEF.

gcc/cp/ChangeLog:

	* parser.cc: Remove unnecessary forward declarations.
	(cp_parser_string_literal): New wrapper.
	(cp_parser_string_literal_common): Renamed from
	cp_parser_string_literal.  Add a bool parameter.  Give an error when
	UDLs are not permitted.
	(cp_parser_userdef_string_literal): New wrapper.
	(finish_userdef_string_literal): Renamed from
	cp_parser_userdef_string_literal.
	(cp_parser_primary_expression): Call cp_parser_userdef_string_literal
	instead of cp_parser_string_literal.
	(cp_parser_linkage_specification): Move a variable declaration closer
	to its first use.
	(cp_parser_static_assert): Likewise.
	(cp_parser_operator): Call cp_parser_userdef_string_literal instead of
	cp_parser_string_literal.
	(cp_parser_asm_definition): Move a variable declaration closer to its
	first use.
	(cp_parser_asm_specification_opt): Move variable declarations closer to
	their first use.
	(cp_parser_asm_operand_list): Likewise.
	(cp_parser_asm_clobber_list): Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/udlit-error1.C: New test.