[clang] [CIR] Accept _BitInt up to 128 bits in x86_64 callconv lowering (PR #212668)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

A few nits, but I don't understand what is going on well enough to approve this one.

https://github.com/llvm/llvm-project/pull/212668