Review on llvm/llvm-project#187484?

[hoodmane]

Would appreciate if @dschuff or @aheejin or anyone could review llvm/llvm-project#187484.

[aheejin]

Sorry for the delay. Will take a look

[guybedford]

Ping @sbc100 and @brendandahl as well - it appears we should either land this or revert rust-lang/rust#151771. Would be great to ensure we're on the path to exception handling stability more generally.