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

[Yingwei Zheng via llvm-commits]

================
@@ -1548,25 +1548,38 @@ template <typename T> inline Exact_match<T> m_Exact(const T &SubPattern) {
 //
 
 template <typename LHS_t, typename RHS_t, typename Class, typename PredicateTy,
-          bool Commutable = false>
+          bool Commutable = false, bool MatchExistingPred = false>
 struct CmpClass_match {
-  PredicateTy &Predicate;
+  static_assert(!Commutable || !MatchExistingPred,
+                "Can't match predicate when using commutable matcher");
+
+  // Make predicate ty const ref if we are matching. Not strictly necessary but
+  // will cause a compilation warning if we accidentally try to set it with
+  // MatchExistingPred enabled.
+  using InternalPredTy =
+      std::conditional_t<MatchExistingPred, const PredicateTy &, PredicateTy &>;
----------------
dtcxzyw wrote:

```suggestion
      std::conditional_t<MatchExistingPred, const PredicateTy, PredicateTy &>;
```
Would be better to pass by value?


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