This patch fixes the following error when building on arm mac.
CMake Error at /Users/tnishinaga/projects/tnishinaga/llvm/llvm-project/openmp/runtime/cmake/LibompGetArchitecture.cmake:74 (file): file failed to open for reading (No such file or directory): /proc/cpuinfo Call Stack (most recent call first): /Users/tnishinaga/projects/tnishinaga/llvm/llvm-project/openmp/runtime/CMakeLists.txt:73 (libomp_is_aarch64_a64fx)