[llvm] [llvm-gsymutil] Address merged-funcs test non-determinism (PR #122308)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

@alx32 https://lab.llvm.org/buildbot/#/builders/16/builds/11878 - there still seems to be some intermittent failures on EXPENSIVE_CHECKS builds - are you relying on any sorting? llvm::sort pre-shuffles the data to check for non-deterministic bugs.

https://github.com/llvm/llvm-project/pull/122308