re PR c/20368 (internal compiler error: tree check: expected function_type or method_type, have integer_type in start_function, at c-decl.c:5777)

	PR c/20368
	* c-decl.c (start_function): Check for old_decl being
	error_mark_node.

testsuite:
	* gcc.dg/pr20368-1.c, gcc.dg/pr20368-2.c, gcc.dg/pr20368-3.c: New
	tests.

From-SVN: r97270