[dev.link] cmd/asm: expand package path if known

[dev.link] cmd/asm: expand package path if known

If the package path is known, pass it to the object file writer
so the symbol names are pre-expanded. (We already expand the
package path in debug info.)

Change-Id: I2b2b71edbb98924cbf3c4f9142b7e109e5b7501a
Reviewed-on: https://go-review.googlesource.com/c/go/+/234491
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>