Auto merge of #112001 - saethlin:enable-matchbranchsimplification, r=cjgillot

Enable MatchBranchSimplification

This pass is one of the small number of benefits from `-Zmir-opt-level=3` that has motivated rustc_codegen_cranelift to use it:

https://github.com/rust-lang/rust/blob/19ed0aade60e1c1038fe40554bcd9d01b717effa/compiler/rustc_codegen_cranelift/build_system/build_sysroot.rs#L244-L246

Cranelift's motivation for this is _runtime_ performance improvements in debug builds. Lifting this pass all the way to `-Zmir-opt-level=1` seems to come without significant perf overhead, so that's what I'm suggesting here.

Author: bors