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

[Shilei Tian via llvm-commits]

shiltian wrote:

That's my point. I think it is much easier for each target to "mind their own business" instead of trying to figuring out which ones are common among multiple other targets and which are not such that I'd need to have my own branch. Originally they are distributed in their own file but I can see the motivation and need to move them here. To have one block for each target can make it much cleaner. Some duplication here doesn't matter IMHO.

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