Xray instrumentation / enabling more tests

Summary:
The Unix subdirectory mostly allows only on Linux x86_64 but now we can target x86_64 arch in general.

Patch by David CARLIER

Reviewers: krytarowski, dberris, emaste

Reviewed By: krytarowski, dberris, emaste

Subscribers: emaste, llvm-commits, #sanitizers

Differential Revision: https://reviews.llvm.org/D43382

llvm-svn: 325743