Revert "[OpenMP] Remove LLVM_ENABLE_PROJECTS=openmp build mode (#152189)"

This reverts commit 20d0ec849804218d75647aeafbe23f8a02a83b56.

The publish-sphinx-docs buildbot still uses LLVM_ENABLE_PROJECTS=openmp.

GitOrigin-RevId: 9ac2d0a9b9ef8893216e8f0b2afb14bcd0a539ff
1 file changed