cmd/link: fix file-local checks in xcoff

The xcoff writer has several "ldr.SymVersion(s) != 0" checks. The
intent of these is to check for file-local (or static) symbols. Prior
to the introduction of symbol ABIs, this was indeed equivalent since
only file-local symbols has non-zero versions, but ABIs also use the
symbol version space. This still happened to work until much more
recently because we were only ever cgo-exporting version 0 symbols,
but CL 309341 changed this, causing these checks to fail on symbols
that were okay to export.

Replace these checks with ldr.IsFileLocal(s).

This should fix the AIX builder.

(Originally based on CL 309772.)

Fixes #45553.
Updates #40724.

Change-Id: I0a3a7f621ad8f9fe078d34e667286275257691ea
Reviewed-on: https://go-review.googlesource.com/c/go/+/310729


Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>