[CUDA] Move CUDA SDK include path further down the include search path.

[tra]

Summary

This allows clang to work on Linux distributions like Debian where
<CUDA-PATH>/include may be a symlink to /usr/include. We only need
cuda_wrappers to be present before the standard C++ library headers.
The CUDA SDK headers themselves do not need to be found that early.

This addresses https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=995122
mentioned in post-commit comments on D108247

[tra]

Fixed the failing test affected by the search path changes.
Disabled addition of CUDA include path if -nogpuinc is in effect.

[tra]

@tambre I've tested the patch on experimental debian docker and it appears to work with a symlink /usr/lib/cuda/include ->/usr/include.

[tambre]

Thank you for your quick turnaround. I can confirm that this works for me on Debian Unstable with my vendored LLVM.

clang/lib/Driver/ToolChains/Cuda.cpp

void CudaInstallationDetector::AddCudaIncludeArgs(
   if (DriverArgs.hasArg(options::OPT_nogpuinc))
     return;
 
   if (!isValid()) {
     D.Diag(diag::err_drv_no_cuda_installation);
     return;
   }
 
-  CC1Args.push_back("-internal-isystem");
-  CC1Args.push_back(DriverArgs.MakeArgString(getIncludePath()));
   CC1Args.push_back("-include");
   CC1Args.push_back("__clang_cuda_runtime_wrapper.h");
 }
 
 void CudaInstallationDetector::CheckCudaVersionSupportsArch(
     CudaArch Arch) const {
   if (Arch == CudaArch::UNKNOWN || Version == CudaVersion::UNKNOWN ||
       ArchsWithBadVersion[(int)Arch])

 ToolChain::CXXStdlibType
 CudaToolChain::GetCXXStdlibType(const ArgList &Args) const {
   return HostTC.GetCXXStdlibType(Args);
 }
 
 void CudaToolChain::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
                                               ArgStringList &CC1Args) const {
   HostTC.AddClangSystemIncludeArgs(DriverArgs, CC1Args);
+
+  if (!DriverArgs.hasArg(options::OPT_nogpuinc) && CudaInstallation.isValid())
+    CC1Args.append(
+        {"-internal-isystem",
+         DriverArgs.MakeArgString(CudaInstallation.getIncludePath())});
 }
 
 void CudaToolChain::AddClangCXXStdlibIncludeArgs(const ArgList &Args,
                                                  ArgStringList &CC1Args) const {
   HostTC.AddClangCXXStdlibIncludeArgs(Args, CC1Args);
 }
 
 void CudaToolChain::AddIAMCUIncludeArgs(const ArgList &Args,

clang/test/Driver/cuda-detect.cu

 // LIBDEVICE-SAME: "-mlink-builtin-bitcode"
 // LIBDEVICE10-SAME: libdevice.10.bc
 // LIBDEVICE20-SAME: libdevice.compute_20.10.bc
 // LIBDEVICE30-SAME: libdevice.compute_30.10.bc
 // LIBDEVICE35-SAME: libdevice.compute_35.10.bc
 // LIBDEVICE50-SAME: libdevice.compute_50.10.bc
 // PTX42-SAME: "-target-feature" "+ptx42"
 // PTX60-SAME: "-target-feature" "+ptx60"
-// CUDAINC-SAME: "-internal-isystem" "{{.*}}/Inputs/CUDA{{[_0-9]+}}/usr/local/cuda/include"
-// NOCUDAINC-NOT: "-internal-isystem" "{{.*}}/cuda/include"
 // CUDAINC-SAME: "-include" "__clang_cuda_runtime_wrapper.h"
 // NOCUDAINC-NOT: "-include" "__clang_cuda_runtime_wrapper.h"
+// CUDAINC-SAME: "-internal-isystem" "{{.*}}/Inputs/CUDA{{[_0-9]+}}/usr/local/cuda/include"
+// NOCUDAINC-NOT: "-internal-isystem" "{{.*}}/cuda/include"
 // -internal-externc-isystem flags must come *after* the cuda include flags,
 // because we must search the cuda include directory first.
 // CUDAINC-SAME: "-internal-externc-isystem"
 // COMMON-SAME: "-x" "cuda"
 // CHECK-CXXINCLUDE: clang{{.*}} "-cc1" "-triple" "nvptx64-nvidia-cuda"
 // CHECK-CXXINCLUDE-SAME: {{.*}}"-internal-isystem" "{{.+}}/include/c++/4.8"
 // CHECK-CXXINCLUDE: clang{{.*}} "-cc1" "-triple" "x86_64-unknown-linux-gnu"
 // CHECK-CXXINCLUDE-SAME: {{.*}}"-internal-isystem" "{{.+}}/include/c++/4.8"