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

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> 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.

We have the same sprawl in the `TargetLibraryInfo`. I didn't think it was large enough to justify factoring it out, especially when so many of these are common already.

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