When calling the testsuite, clang could not locate omp.h. The
proper environment variable was modified to include:
exports/common/omp.h. Documentation was also updated to be more
clear.
Patch by Sunita Chandrasekaran
git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@237618 91177308-0d34-0410-b5e6-96231b3b80d8