[clang] [mlir] [CIR] Honor the Direct coercion offset in x86_64 callconv lowering (PR #220724)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

Can't say I really udnerstand this well enough, so we'll need a better set of eyes, but the IR looks reasonable enough? 

https://github.com/llvm/llvm-project/pull/220724