[libomptarget-nvptx-bc] Pass found CUDA installations

We already know where the CUDA SDK is, so there is no point in
letting Clang search for it again and possibly finding no or
a different installation.

--cuda-path is supported since the beginning of CUDA support in
Clang, so making this required doesn't impose additional restrictions.

Differential Revision: https://reviews.llvm.org/D46930

llvm-svn: 332495

Author: hahnjo

openmp/libomptarget/cmake/Modules/LibomptargetNVPTXBitcodeLibrary.cmake

@@ -79,7 +79,7 @@ endfunction()
 
 # These flags are required to emit LLVM Bitcode. We check them together because
 # if any of them are not supported, there is no point in finding out which are.
-set(compiler_flags_required -emit-llvm -O1 --cuda-device-only)
+set(compiler_flags_required -emit-llvm -O1 --cuda-device-only --cuda-path=${CUDA_TOOLKIT_ROOT_DIR})
 set(compiler_flags_required_src "extern \"C\" __device__ int thread() { return threadIdx.x; }")
 check_bitcode_compilation(LIBOMPTARGET_NVPTX_CUDA_COMPILER_SUPPORTS_FLAGS_REQUIRED "${compiler_flags_required_src}" ${compiler_flags_required})