add smallpt benchmark to test-suite

original source from http://www.kevinbeason.com/smallpt/ with the following
modifications:
- commented out openmp pragma
- disabled writing to output image to file


git-svn-id: https://llvm.org/svn/llvm-project/test-suite/trunk@171745 91177308-0d34-0410-b5e6-96231b3b80d8