This CL also make cmd/nm accept PE object file.

Fixes #21706

Change-Id: I4a528b7d53da1082e61523ebeba02c4c514a43a7
Reviewed-on: https://go-review.googlesource.com/64890
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>