[cfi] Help sanstats to find binary if they are not at the original location

Summary:
By default sanstats search binaries at the same location where they were when
stats was collected. Sometime you can not print report immediately or you need
to move post-processing to another workstation. To support this use-case when
original binary is missing sanstats will fall-back to directory with sanstats
file.

Reviewers: pcc

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D53857

llvm-svn: 347601