CUDA: Clang CUDA 11.1 support

version.txt is gone from CUDA 11.1 installations, but the rest is the same.
Instead of looking for version.txt look for <CUDA path>/nvvm/libdevice, which
is the main thing that Clang requires (though it also checks for the existence
of bin and include).

Fixes #21353.

Help/release/3.19.rst

@@ -346,3 +346,5 @@ Changes made since CMake 3.19.0 include the following.
   it can break projects that were using the property only to
   cause the specified language's compiler to be used.  This has
   been reverted to restore behavior from CMake 3.18 and below.
+
+* CUDA 11.1 support for Clang.

Modules/CMakeDetermineCUDACompiler.cmake

@@ -176,12 +176,12 @@ if(NOT CMAKE_CUDA_COMPILER_ID_RUN)
     # In a non-scattered installation the following are equivalent to CMAKE_CUDA_COMPILER_TOOLKIT_ROOT.
     # We first check for a non-scattered installation to prefer it over a scattered installation.
 
-    # CMAKE_CUDA_COMPILER_LIBRARY_ROOT contains the device library and version file.
-    if(EXISTS "${CMAKE_CUDA_COMPILER_TOOLKIT_ROOT}/version.txt")
+    # CMAKE_CUDA_COMPILER_LIBRARY_ROOT contains the device library.
+    if(EXISTS "${CMAKE_CUDA_COMPILER_TOOLKIT_ROOT}/nvvm/libdevice")
       set(CMAKE_CUDA_COMPILER_LIBRARY_ROOT "${CMAKE_CUDA_COMPILER_TOOLKIT_ROOT}")
-    elseif(CMAKE_SYSROOT_LINK AND EXISTS "${CMAKE_SYSROOT_LINK}/usr/lib/cuda/version.txt")
+    elseif(CMAKE_SYSROOT_LINK AND EXISTS "${CMAKE_SYSROOT_LINK}/usr/lib/cuda/nvvm/libdevice")
       set(CMAKE_CUDA_COMPILER_LIBRARY_ROOT "${CMAKE_SYSROOT_LINK}/usr/lib/cuda")
-    elseif(EXISTS "${CMAKE_SYSROOT}/usr/lib/cuda/version.txt")
+    elseif(EXISTS "${CMAKE_SYSROOT}/usr/lib/cuda/nvvm/libdevice")
       set(CMAKE_CUDA_COMPILER_LIBRARY_ROOT "${CMAKE_SYSROOT}/usr/lib/cuda")
     endif()