[Sanitizer] Add a test for the fast unwinder

Summary:
The test sets up fake x86-style fp+retaddr frames, since that's all the
unwinder works with.

Reviewers: kcc

CC: eugenis

Differential Revision: http://llvm-reviews.chandlerc.com/D445

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@175893 91177308-0d34-0410-b5e6-96231b3b80d8