Auto merge of #144347 - scottmcm:ssa-enums-v0, r=WaffleLapkin

No longer need `alloca`s for consuming `Result<!, i32>` and similar

In optimized builds GVN gets rid of these already, but in `opt-level=0` we actually make `alloca`s for this, which particularly impacts `?`-style things that use actually-only-one-variant types like this.

While doing so, rewrite `LocalAnalyzer::process_place` to be non-recursive, solving a 6+ year old FIXME.

r? codegen

Author: bors