[dev.cc] cmd/go: run C and Go assemblers side by side and verify matching output
When an assembly file must be assembled, cmd/go now runs
both (say) 6a and new6a and checks that they write identical
output files.
This serves as a build-time test that the new assemblers are accurate
conversions of the old ones. As long as they are producing identical
bytes, there's no need for run-time testing.
Once the C conversion is done, we'll throw away the C code
and this checking.
Change-Id: I0216dad56b7e79011eecd27f1aff4fe79bfe720b
Reviewed-on: https://go-review.googlesource.com/3145 Reviewed-by: Rob Pike <r@golang.org>