[CMake] Print out the list of sanitizers that the sanitizer_common tests will run against.

Summary:
This is a change requested by Vitaly Buka as prerequisite to landing
https://reviews.llvm.org/D55740.

Reviewers: vitalybuka, kubamracek

Subscribers: mgorny, #sanitizers, llvm-commits

Differential Revision: https://reviews.llvm.org/D55939

llvm-svn: 349897