[AArch64] front-end crash when using -mcmodel=medium flag on clang

[jdomke]

LLVM v13.0.0
Easy to reproduce: touch foo.c ; clang --target=aarch64 -mcmodel=medium -c foo.c
Yields:

fatal error: error in backend: Only small, tiny and large code models are allowed on AArch64
PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.	Program arguments: /home/ra000004/a04018/llvm-v13.0.0/login_node/bin/clang -mcmodel=medium -c foo.c
1.	<eof> parser at end of file
 #0 0x0000000001702af3 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/home/ra000004/a04018/llvm-v13.0.0/login_node/bin/clang+0x1702af3)
...

[llvmbot]

@llvm/issue-subscribers-backend-aarch64

[Hsiangkai]

I filter out the invalid code model in the clang driver. https://reviews.llvm.org/D132538

[llvmbot]

@llvm/issue-subscribers-clang-driver