cmd/link: deal with ADDR32NB relocations the same way as ADDR32 on arm

As far as I can tell, the addend is the same for both of these, and in
this context we don't really care about setting or unsetting the thumb
selection bit, so just treat these the same way.

Change-Id: I3756c027239f77778c32b317733df9ac92272580
Reviewed-on: https://go-review.googlesource.com/c/go/+/268238


Reviewed-by: Cherry Zhang <cherryyz@google.com>
Trust: Jason A. Donenfeld <Jason@zx2c4.com>