Always build CUDA on CI. (#8867)

Adds a special case to detect when the stripped down CUDA deps on our CI
images are available and uses that (i.e. a full SDK will not detect in
this case).

Fixes #8847
diff --git a/CMakeLists.txt b/CMakeLists.txt
index b320b20..8a39a47 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -362,6 +362,15 @@
 # back to this as needed for specific features.
 if(IREE_TARGET_BACKEND_CUDA OR IREE_HAL_DRIVER_CUDA)
   find_package(CUDAToolkit)
+
+  # We define the magic IREE_CUDA_DEPS_DIR env var in our CI docker images if we
+  # have a stripped down CUDA toolkit suitable for compiling available. We
+  # trigger on this below as a fallback for locating headers and libdevice
+  # files.
+  if(NOT CUDAToolkit_FOUND AND DEFINED ENV{IREE_CUDA_DEPS_DIR})
+    set(CUDAToolkit_ROOT "$ENV{IREE_CUDA_DEPS_DIR}")
+    message(STATUS "CUDA SDK not found by CMake but using IREE_CUDA_DEPS = ${CUDAToolkit_ROOT}")
+  endif()
 endif()
 
 # If an explicit libdevice file was not specified, and the compiler backend