cmd/link: eliminate a bunch of open coded elf64/rela switches
We already have variables to track whether the target platform is
64-bit vs 32-bit or RELA vs REL, so no point in repeating the list of
obscure architecture characters everywhere.
Passes toolstash/buildall.
Change-Id: I6a07f74188ac592ef229a7c65848a9ba93013cdb
Reviewed-on: https://go-review.googlesource.com/21569
Run-TryBot: Matthew Dempsky <mdempsky@google.com> Reviewed-by: Michael Hudson-Doyle <michael.hudson@canonical.com> Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>