[Offload] Fix using old deprecated CUDA root variable (#96307)

Summary:
This variable isn't being set properly since we moved to the new way to
find the CUDA directory. That means this variable was just unset the
whole time. This patch adds it in by calculating it using the binary
directory so it can be passed to `--cuda-path`.

Author: jhuber6

offload/test/CMakeLists.txt

@@ -16,6 +16,12 @@ endif()
 # char into the lit command.
 string(REPLACE " " ";" LIBOMPTARGET_LIT_ARG_LIST "${LIBOMPTARGET_LIT_ARGS}")
 
+find_package(CUDAToolkit QUIET)
+if(CUDAToolkit_FOUND)
+  get_filename_component(CUDA_ROOT "${CUDAToolkit_BIN_DIR}" DIRECTORY ABSOLUTE)
+  get_filename_component(CUDA_LIBDIR "${CUDA_cudart_static_LIBRARY}" DIRECTORY)
+endif()
+
 string(REGEX MATCHALL "([^\ ]+\ |[^\ ]+$)" SYSTEM_TARGETS "${LIBOMPTARGET_SYSTEM_TARGETS}")
 foreach(CURRENT_TARGET IN LISTS SYSTEM_TARGETS)
   string(STRIP "${CURRENT_TARGET}" CURRENT_TARGET)
@@ -29,7 +35,6 @@ foreach(CURRENT_TARGET IN LISTS SYSTEM_TARGETS)
 
   # Configure the lit.site.cfg.in file
   set(AUTO_GEN_COMMENT "## Autogenerated by libomptarget configuration.\n# Do not edit!")
-  get_filename_component(CUDA_LIBDIR "${CUDA_cudart_static_LIBRARY}" DIRECTORY)
   configure_file(lit.site.cfg.in ${CURRENT_TARGET}/lit.site.cfg @ONLY)
 endforeach()
 

offload/test/lit.site.cfg.in

@@ -7,7 +7,7 @@ config.test_fortran_compiler="@OPENMP_TEST_Fortran_COMPILER@"
 config.test_compiler_features = @OPENMP_TEST_COMPILER_FEATURES@
 config.test_openmp_flags = "@OPENMP_TEST_OPENMP_FLAGS@"
 config.test_extra_flags = "@OPENMP_TEST_FLAGS@"
-config.cuda_path = "@CUDA_TOOLKIT_ROOT_DIR@"
+config.cuda_path = "@CUDA_ROOT@"
 config.cuda_libdir = "@CUDA_LIBDIR@"
 config.cuda_test_arch = "@LIBOMPTARGET_DEP_CUDA_ARCH@"
 config.amdgpu_test_arch = "@LIBOMPTARGET_AMDGPU_DETECTED_ARCH_LIST@"