[Misc][ROCm] Enforce no unused variable in ROCm C++ files (vllm-project#19796)

Signed-off-by: Lu Fang <lufang@fb.com>
Signed-off-by: minpeter <kali2005611@gmail.com>

Author: houseroad

cmake/utils.cmake

@@ -122,6 +122,7 @@ function (get_torch_gpu_compiler_flags OUT_GPU_FLAGS GPU_LANG)
       "-DENABLE_FP8"
       "-U__HIP_NO_HALF_CONVERSIONS__"
       "-U__HIP_NO_HALF_OPERATORS__"
+      "-Werror=unused-variable"
       "-fno-gpu-rdc")
 
   endif()