[llvm] [coverage] Add option for keeping mappings order (PR #91600)

[Alan Phipps via llvm-commits]

evodius96 wrote:

Thanks for tackling this and the explanation.

I'm wondering if we should also go ahead and add support in clang. It would certainly make it easier to test with cases in `compiler-rt/test/profile` where we can generate, run, and visualize everything.

> Sure I should try to learn how to write some unit cases. Considering we can not call rustc here, are some mock mappings appropriate?

You might also create LIT cases in `llvm/test/tools/llvm-cov` for llvm-cov that rely on text-formatted profdata files for a mock example.  But it'd be better to avoid relying on prebuilt binaries, if possible.  I'd like to see what others suggest.

https://github.com/llvm/llvm-project/pull/91600