[ASan] Make stack-buffer-overflow reports more robust

Summary:
Fix the function that gets stack frame description by address in
thread stack, so that it clearly indicates failures. Make this error non-fatal,
and print as much information as we can in this case. Make all errors in
ParseFrameDescription non-fatal.

Test Plan: check-asan testsuite

Reviewers: kcc

Reviewed By: kcc

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D5554