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

[Matt Arsenault via llvm-commits]

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

LGTM but I think this should add a new test for the full set of memory intrinsics which should now be expanded 

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