[llvm] RuntimeLibcalls: Add provider libraries for targets to reference (PR #229562)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> I've lost track of this set of changes. Looks ... complicated. Is there any documentation on the concepts used (e.g. "provider library") and what changes needs to be made when adding a new target support?

It's just a library that provides the function. We have a flat list and don't know the name of the binary which is needed to define the function 

https://github.com/llvm/llvm-project/pull/229562