[clang] Fix CGObjCGNU __cxa_rethrow return type (PR #214496)

[Hendrik Hübner via cfe-commits]

HendrikHuebner wrote:

@davidchisnall Yep, seems like a copy paste issue. I need this fixed to upstream the WASM exception support @hmelder started. I will send some patches later this week.

https://github.com/llvm/llvm-project/pull/214496