TestDWARF has been added in CL 38855. This test is
failing on Plan 9 because executables don't have
a DWARF symbol table.

Fixes #19793.

(This fixes Plan 9 failures on the release branch introduced by
cherry-pick CL 39605.)

Change-Id: I7fc547a7c877b58cc4ff6b4eb5b14852e8b4668b
Reviewed-on: https://go-review.googlesource.com/39611
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>