[WebAssembly] Fix a non-determinism problem in FixIrreducibleControlFlow

Summary:
We already sorted the blocks when fixing up a set of mutual
loop entries, however, there can be multiple sets of such
mutual loop entries, and the order we encounter them
should not be random, so sort them too.

Fixes https://bugs.llvm.org/show_bug.cgi?id=44982

Patch by Alon Zakai (kripken)

Reviewers: aheejin, sbc100, dschuff

Subscribers: mgrang, sunfish, hiraditya, jgravelle-google, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D74999