Fix build failure on GCC (#20231)

Use function overload instead of explicit specialization to fix GCC
error:

```
/__w/iree/iree/compiler/src/iree/compiler/Utils/OptionUtils.h:58:13: error: explicit specialization in non-namespace scope 'struct mlir::iree_compiler::opt_initializer<Ty>'
   58 |   template <>
      |          
```

Signed-off-by: Ian Wood <[email protected]>

Author: IanWood1

compiler/src/iree/compiler/Utils/OptionUtils.h

@@ -55,8 +55,7 @@ struct opt_initializer {
     os << val;
   }
 
-  template <>
-  void prettyPrint<bool>(llvm::raw_ostream &os, bool &val) {
+  void prettyPrint(llvm::raw_ostream &os, bool &val) {
     os << (val ? "true" : "false");
   }
 };