Darwin linker does not support BR26 reloc with non-zero addend.

Fixes #16724.

Change-Id: I1b5b4dc7159141bde3e273490f435c08c583afaf
Reviewed-on: https://go-review.googlesource.com/27081
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dave Cheney <dave@cheney.net>