[llvm] [NFC][EarlyIfConverter] Replace boolean Preadicate for a class (PR #108519)

[Thorsten Schütt via llvm-commits]

================
@@ -122,6 +122,17 @@ class SSAIfConv {
   /// The branch condition determined by analyzeBranch.
   SmallVector<MachineOperand, 4> Cond;
 
+  struct PredicationStrategyBase {
----------------
tschuett wrote:

`struct` with inheritance, virtual methods, and `=0`  is really confusing.

https://github.com/llvm/llvm-project/pull/108519