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

[Peter Smith via cfe-commits]

https://github.com/smithp35 commented:

I'm happy with this on the AArch64 side.

If clang for a target defaults to position independent code this may lead to some -mcmodel=large projects failing to build, at least until they add -fno-pic 

Could we add this to the release notes? Perhaps in the form that users of -mcmodel=large on AArch64 are recommended to add -fno-pic.

I think this is better than -mcmodel=large silently producing non position independent code. 

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