[llvm-mca] Add an error handler for error from parseCodeRegions

Summary:
It's a bit tricky to add a test for the failing path right now, binary support will have an easier path to exercise the path here.

* Ran clang-format.



Reviewers: andreadb

Reviewed By: andreadb

Subscribers: tschuett, gbedwell, llvm-commits

Differential Revision: https://reviews.llvm.org/D55803

llvm-svn: 349659