[SYCL] Use CUDA_PATH as a candidate for path discovery (#5194)

Author: jchlanda

clang/lib/Driver/ToolChains/Cuda.cpp

@@ -136,6 +136,11 @@ CudaInstallationDetector::CudaInstallationDetector(
     Candidates.emplace_back(
         Args.getLastArgValue(clang::driver::options::OPT_cuda_path_EQ).str());
   } else if (HostTriple.isOSWindows()) {
+    // CUDA_PATH is set by the installer, prefer it over other versions that
+    // might be present on the system.
+    if (const char *CudaPathEnvVar = ::getenv("CUDA_PATH"))
+      Candidates.emplace_back(CudaPathEnvVar);
+
     for (const char *Ver : Versions)
       Candidates.emplace_back(
           D.SysRoot + "/Program Files/NVIDIA GPU Computing Toolkit/CUDA/v" +

clang/test/Driver/cuda-windows-cuda-path.cpp

@@ -0,0 +1,11 @@
+///
+/// Make sure that CUDA_PATH is picked up correctly when looking for CUDA
+/// installation.
+///
+
+// REQUIRES: system-windows
+// RUN: env CUDA_PATH=%S\Inputs\CUDA_111\usr\local\cuda %clang -fsycl \
+// RUN: -fsycl-targets=nvptx64-nvidia-cuda -### -v %s 2>&1 | \
+// RUN: FileCheck %s
+
+// CHECK: Found CUDA installation: {{.*}}Inputs\CUDA_111\usr\local\cuda, version 11.1