Revert "Fix missing build dependency on omp_gen."
This reverts commit ed4328c607306a2aa6df4833a0dce4482edbc94c.
My change apparently caused a buildbot to fail with the error
CMake Error at /b/sanitizer-x86_64-linux-autoconf/build/tsan_release_build/lib/cmake/llvm/AddLLVM.cmake:869 (add_dependencies): The dependency target "omp_gen" of target "ScudoBenchmarks.x86_64" does not exist.
I don't at all understand why, because as far as I can see, the target
omp_gen is only added to LLVM_COMMON_DEPENDS after having been
created, so there should be no way it can end up on anything's
dependency list if it doesn't exist! But apparently it happened anyway.
Differential Revision: https://reviews.llvm.org/D82659