-fgo-dump-spec: skip typedefs that match struct tag

-fgo-dump-spec: skip typedefs that match struct tag

gcc/:
	* godump.c (go_output_typedef): Suppress typedefs whose name
	matches the tag of the underlying struct, union, or enum.
	Output declarations for enums that do not appear in typedefs.
gcc/testsuite:
	* gcc.misc-tests/godump-1.c: Add test cases.