Use LLVM dynamic dispatch to disambiguate between StmtBlock subclasses.

PiperOrigin-RevId: 204614520
diff --git a/lib/IR/Function.cpp b/lib/IR/Function.cpp
index 453797f..72ec443 100644
--- a/lib/IR/Function.cpp
+++ b/lib/IR/Function.cpp
@@ -48,5 +48,4 @@
 //===----------------------------------------------------------------------===//
 
 MLFunction::MLFunction(StringRef name, FunctionType *type)
-  : Function(name, type, Kind::MLFunc), StmtBlock() {
-}
+    : Function(name, type, Kind::MLFunc), StmtBlock(StmtBlockKind::MLFunc) {}