Rollup merge of #117744 - quininer:add-z-sync-uw, r=bjorn3

Add -Zuse-sync-unwind

Currently Rust uses async unwind by default, but async unwind will bring non-negligible size overhead. it would be nice to allow users to choose this.

In addition, async unwind currently prevents LLVM from generate compact unwind for MachO, if one wishes to generate compact unwind for MachO, then also needs this flag.

Author: matthiaskrgr