[msan] Fix potential infinite recursion in a test.

If printf is intercepted (it is not atm), REAL(printf) call in the interceptor
would get redirected back to my_lgamma, resulting in infinite recursion.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@208294 91177308-0d34-0410-b5e6-96231b3b80d8