[llvm] [TLI] Add support for lgamma libcall. (PR #114536)

[via llvm-commits]

ZERICO2005 wrote:

I have plans to add `KnownFPClass::lgamma` in the future after this PR is merged https://github.com/llvm/llvm-project/pull/216234, which would rely on detecting `lgamma` as a `LibFunc` through `TargetLibraryInfo`.

Is this PR still wanted? I would be interested in helping revive this if needed.

https://github.com/llvm/llvm-project/pull/114536