runtime: run the right test in TestCgoExternalThreadSignal
The code was accidentally repeating the TestCgoExternalThreadSIGPROF test.
While we're here remove an obsolete skip on ppc64/linux.
Change-Id: Icdc4032a67aa80fbcfcd7c5c7ab8a6f23f321e2e
Reviewed-on: https://go-review.googlesource.com/c/go/+/366755
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Bryan C. Mills <bcmills@google.com>