Implement operands for the 'if' statement.

This CL also includes two other minor changes:
- change the implemented syntax from 'if (cond)' to 'if cond', as specified by MLIR spec.
- a minor fix to the implementation of the ForStmt.

PiperOrigin-RevId: 210618122
diff --git a/lib/IR/Builders.cpp b/lib/IR/Builders.cpp
index 8d0f223..a03de2f 100644
--- a/lib/IR/Builders.cpp
+++ b/lib/IR/Builders.cpp
@@ -254,8 +254,9 @@
   return stmt;
 }
 
-IfStmt *MLFuncBuilder::createIf(Location *location, IntegerSet *condition) {
-  auto *stmt = new IfStmt(location, condition);
+IfStmt *MLFuncBuilder::createIf(Location *location,
+                                ArrayRef<MLValue *> operands, IntegerSet *set) {
+  auto *stmt = IfStmt::create(location, operands, set);
   block->getStatements().insert(insertPoint, stmt);
   return stmt;
 }