[MIPS]: Don't terminate stackwalk when $sp value doesn't change between frames

Currently on MIPS we accidentally terminate stackwalk if $sp value doesn't change between frames 
which results in incomplete callchain terminated at the point of first tailcall encountered.

Change-Id: I8f1ed1df958d8f0a9eb11fd7800062184d8f1ee2
Reviewed-on: https://chromium-review.googlesource.com/449755
Reviewed-by: Mark Mentovai <mark@chromium.org>
Cr-Mirrored-From: https://chromium.googlesource.com/breakpad/breakpad
Cr-Mirrored-Commit: 796a6c9baf85bf3ee15bba8fdbf0c5355a609597
3 files changed