[clang] [llvm] [clang][PowerPC] Support the Swift calling convention on 32-bit PowerPC (PR #213447)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> @AaronBallman this generally looked "reasonable", but the last time PPC was in 2024 by @syzaara and I'm not sure if they're following llvm at all anymore

I'm surprised to see interest in 32-bit PPC, but it is a target that LLVM still supports. That said, I think we need to hear from two groups:

1) A Swift maintainer to validate that they want this calling convention supported. CC @rjmccall @compnerd @ojhunt (feel free to rope in someone more appropriate!) We should probably have someone listed as a maintainer (or point of contact) for Swift in the Clang maintainers file because Swift-related topics come up from time to time. WDYT? Any volunteers?
2) A PPC maintainer to validate the PPC32 ABI CC @llvmonpower @lei137 


https://github.com/llvm/llvm-project/pull/213447