runtime, runtime/pprof: add Frames to get file/line for Callers

runtime, runtime/pprof: add Frames to get file/line for Callers

This indirectly implements a small fix for runtime/pprof: it used to
look for runtime.gopanic when it should have been looking for
runtime.sigpanic.

Update #11432.

Change-Id: I5e3f5203b2ac5463efd85adf6636e64174aacb1d
Reviewed-on: https://go-review.googlesource.com/19869
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>