[clang] [llvm] [AIX] Add -msave-reg-params to save arguments to stack (PR #97524)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

The question is, if LTO merges two bitcode modules together with different settings for the flag, how do you want the backend to behave?  Usually you want it to just continue to apply to the same functions it would have without LTO; the only way to represent that is a function attribute.

https://github.com/llvm/llvm-project/pull/97524