c/c++, asm: Use nicer error for const and restrict

c/c++, asm: Use nicer error for const and restrict

Not all qualifiers are asm qualifiers.  We can talk about that in a
nicer way than just giving a generic parser error.

This also adds two testcases for C++, that previously were for C only.

c/
	* c-parser.c (c_parser_asm_statement) <RID_CONST, RID_RESTRICT>: Give
	a more specific error message (instead of just falling through).

cp/
	* parser.c (cp_parser_asm_definition) <RID_CONST, RID_RESTRICT>: Give
	a more specific error message (instead of just falling through).

testsuite/
	* g++.dg/asm-qual-1.C: New testcase.
	* g++.dg/asm-qual-2.C: New testcase.
	* gcc.dg/asm-qual-1.c: Update.

From-SVN: r267279