Add MLFunction::getReturnStmt.

PiperOrigin-RevId: 208514441
diff --git a/lib/IR/Function.cpp b/lib/IR/Function.cpp
index 4719b35..1c89de8 100644
--- a/lib/IR/Function.cpp
+++ b/lib/IR/Function.cpp
@@ -152,3 +152,11 @@
   this->~MLFunction();
   free(this);
 }
+
+const OperationStmt *MLFunction::getReturnStmt() const {
+  return cast<OperationStmt>(&back());
+}
+
+OperationStmt *MLFunction::getReturnStmt() {
+  return cast<OperationStmt>(&back());
+}