[compiler-rt] Activate interception unittests

Summary:
The unittests recently added were not running when executing 'check-all'.
Tests are stable on every archictetures and we can now turn them on.

Reviewers: rnk

Subscribers: llvm-commits, wang0109, chrisha

Differential Revision: https://reviews.llvm.org/D22695

llvm-svn: 276881