[llvm] [Statepoint] Optimize Location structure size (PR #78600)

[via llvm-commits]

https://github.com/dantrushin approved this pull request.

Looks good.
Suggestion for future improvement:
Change return type of getDwarfRegNumber (in StackMaps.cpp) to uint16_t and add assert that number it gets from TRI really fits in uint16_t


https://github.com/llvm/llvm-project/pull/78600