[llvm] [GSYM] Add support for querying merged functions in llvm-gsymutil (PR #120991)

[via llvm-commits]

alx32 wrote:

Ah interesting, what build environment / machine is this ? 

It produces paths like:
```
/tmp/test_gsym_yaml\out/file_01.cpp:5
```
But the tests expects:
```
 /tmp/test_gsym_yaml/out/file_01.cpp:5 
 ```
 
 Notice the `/` vs `\` in `\out/` vs `/out/`

https://github.com/llvm/llvm-project/pull/120991