cmd/link: sort the pclntab relocations

llvm-mingw's lld produces an invalid windows/arm64 executable
when presented with relocations that are out of order
(the relocation for each function is emitted for two different
locations, so we end up with two sorted streams roughly
interlaced, not one sorted stream).

Sorting should not break other systems, so sort always.

Change-Id: Ic9a95e7145881db5984cbda442f27b0cc24748fb
Reviewed-on: https://go-review.googlesource.com/c/go/+/312033


Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>