[llvm] [PatternMatch] Add matchers for `m_{I,F,}Cmp` and `m_{I,F,}SpecificCmp`; NFC (PR #98282)

[Nikita Popov via llvm-commits]

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

LGTM. We might also need m_c_SpecificICmp, but let's start with this.

https://github.com/llvm/llvm-project/pull/98282