[llvm] [BPF] Define empty set of BPF libcalls (PR #169537)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Yeah the other PR to remove the error also achieves this right?

I do not believe that is a suitable mechanism for achieving that. It would be better to unconditionally remove the error than make it conditional on a subtarget feature

> The way I see it you're taking away some functionality.

I see this as the functionality which does not exist; I do not think it is reasonable to rely on the output of a compile result that hard errored for any reason. If the scope of your issue is only the 3 memory libcalls, I would suggest to start by defining the ABI here by including those and only those calls in the list here. This will avoid failure in an the other odd cases, like the 128-bit libcalls, but maintain those (sans the current error)

https://github.com/llvm/llvm-project/pull/169537