re PR c/20402 (gcc.dg/noncompile/920923-1.c ICE)

	PR c/20402
	* c-parser.c (c_parser_struct_or_union_specifier): Don't fall
	through into call to parser_xref_tag after parse error.
	(c_parser_struct_declaration): Consistently return NULL_TREE on
	error.

testsuite:
	* gcc.dg/noncompile/920923-1.c: Detail expected diagnostics for
	new parser.

From-SVN: r96363