Windows has supported external linking for a while, there is no
need to skip this test.

Change-Id: Ic3d0cc3441ee670767dae085db5e62fce205ff04
Reviewed-on: https://go-review.googlesource.com/c/go/+/480417


Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Quim Muntal <quimmuntal@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>