[Driver,test] Add --target= to unsupported-option-gpu.c

Author: MaskRay

clang/test/Driver/unsupported-option-gpu.c

@@ -1,5 +1,5 @@
 /// Some target-specific options are ignored for GPU, so %clang exits with code 0.
-// DEFINE: %{check} = %clang -### -c -mcmodel=medium
+// DEFINE: %{check} = %clang -### --target=x86_64-linux-gnu -c -mcmodel=medium
 
 // RUN: %{check} -x cuda %s --cuda-path=%S/Inputs/CUDA/usr/local/cuda --offload-arch=sm_60 --no-cuda-version-check -fbasic-block-sections=all
 // RUN: %{check} -x hip %s --rocm-path=%S/Inputs/rocm -nogpulib -nogpuinc