CL 122515 tightened TestAbort to look for breakpoint exceptions and
not just general signal crashes, but this only applies on x86 arches.
On non-x86 arches we use a nil pointer dereference to abort, so the
test is now failing.

This CL re-loosens TestAbort on non-x86 arches to only expect a signal
traceback.

Should fix the build on linux/arm, linux/arm64, linux/ppc64, and
linux/s390x.

Change-Id: I1065341180ab5ab4da63b406c641dcde93c9490b
Reviewed-on: https://go-review.googlesource.com/122580
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>