[Bugfix][Build][Non-CUDA] Only referencing CMAKE_CUDA_COMPILER_VERSION on CUDA...

[Bugfix][Build][Non-CUDA] Only referencing CMAKE_CUDA_COMPILER_VERSION on CUDA where it is defined (#20738)
Signed-off-by: Gregory Shtrasberg <Gregory.Shtrasberg@amd.com>

CMakeLists.txt

@@ -174,8 +174,10 @@ endif()
 #
 # Set nvcc fatbin compression.
 #
-if(${CMAKE_CUDA_COMPILER_VERSION} VERSION_GREATER_EQUAL 12.8 AND VLLM_GPU_LANG STREQUAL "CUDA")
-  list(APPEND VLLM_GPU_FLAGS "-Xfatbin" "-compress-all" "-compress-mode=size")
+if(VLLM_GPU_LANG STREQUAL "CUDA")
+  if(${CMAKE_CUDA_COMPILER_VERSION} VERSION_GREATER_EQUAL 12.8)
+    list(APPEND VLLM_GPU_FLAGS "-Xfatbin" "-compress-all" "-compress-mode=size")
+  endif()
 endif()