We no longer rely on HIPIFY_CLANG_LLVM_DIR to disable hipify-clang
We no longer rely on HIPIFY_CLANG_LLVM_DIR to disable hipify-clang

Since there's now an option for toggling hipify-clang, omitting the
path is no longer something we need to check for. We'll still
abort if LLVM isn't found, due to `REQUIRED`.

GPUOpen-ProfessionalCompute-Tools/HIP,GPUOpen-ProfessionalCompute-Tools/HIP,GPUOpen-ProfessionalCompute-Tools/HIP,ROCm-Developer-Tools/HIP,GPUOpen-ProfessionalCompute-Tools/HIP,ROCm-Developer-Tools/HIP,ROCm-Developer-Tools/HIP,GPUOpen-ProfessionalCompute-Tools/HIP,ROCm-Developer-Tools/HIP,ROCm-Developer-Tools/HIP