[llvm] [LLVM] Factor disabled Libcalls into the initializer (PR #98421)

[Shilei Tian via llvm-commits]

https://github.com/shiltian commented:

I think this handling makes it more difficult to maintain. A better alternative would be to have one code block for each target, just as how they are spread in multiple files.

https://github.com/llvm/llvm-project/pull/98421