Add tf_control type and allow $ in bare-id.

* Add tf_control as primitive type;
* Allow $ in bare-id to allow attributes with $ (to make it trivially to mangle a TF attribute);

PiperOrigin-RevId: 206342642
diff --git a/lib/IR/Builders.cpp b/lib/IR/Builders.cpp
index d5b85cc..a3ad431 100644
--- a/lib/IR/Builders.cpp
+++ b/lib/IR/Builders.cpp
@@ -47,6 +47,10 @@
 
 PrimitiveType *Builder::getF64Type() { return Type::getF64(context); }
 
+PrimitiveType *Builder::getTFControlType() {
+  return Type::getTFControl(context);
+}
+
 IntegerType *Builder::getIntegerType(unsigned width) {
   return Type::getInteger(width, context);
 }