Add trivial golden test that verifies output matches expectation.
The input is based on the old grammar and is intended to cover
the space of the input language.

PPC64 and ARM only for now; others to follow.

Change-Id: Ib5957822bcafd5b9d4c1dea1c03cc6ee1238f7ef
Reviewed-on: https://go-review.googlesource.com/5421Reviewed-by: Russ Cox <rsc@golang.org>