InstrProf: Add simple compiler-rt test

Add the test infrastructure for testing lib/profile and a single test.
This initial commit only enables the tests on Darwin, but they'll be
enabled on Linux soon after.

<rdar://problem/16458307>

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@205256 91177308-0d34-0410-b5e6-96231b3b80d8