Rollup merge of #39319 - nagisa:remove-rustsetpersonalityfn, r=pnkfelix

Remove unnecessary LLVMRustPersonalityFn binding

LLVM Core C bindings provide this function for all the versions back to what we support (3.7), and
helps to avoid this unnecessary builder->function transition every time. Also a negative diff.

Fixes #38462 (although it was pretty much fixed already)