[clang] [Driver] Reject unsupported -mcmodel= (PR #70262)

[Pravin Jagtap via cfe-commits]

pravinjagtap wrote:

This is not being handled for AMDGPU Targets.  @arsenm @yxsamliu @kzhuravl @ronlieb 

Is following case correct for AMDGPU Target ? I am not sure about the previous state before this change for AMGPU Target.
``` 
...
else if (Triple.getArch() == llvm::Triple::amdgcn) {
      Ok = llvm::is_contained({"small", "kernel", "medium", "large", "tiny"},
                              CM);
 }
...
  ```  

https://github.com/llvm/llvm-project/pull/70262