From: Adam Litke <agl@us.ibm.com>

Teach the x86 stack tracing code to use frame pointers, if they are available.
It eliminates all the false-positives in the normal stack traces.

This is a big improvement, and -fomit-frame-pointer seems to make no
difference at all to generated code size.  Maybe we should kill off
-fomit-frame-pointer.