Implement call and call_indirect ops.

This also fixes an infinite recursion in VariadicOperands that this turned up.

PiperOrigin-RevId: 209692932
diff --git a/lib/IR/Builders.cpp b/lib/IR/Builders.cpp
index b1dce25..73beea6 100644
--- a/lib/IR/Builders.cpp
+++ b/lib/IR/Builders.cpp
@@ -111,7 +111,7 @@
   return TypeAttr::get(type, context);
 }
 
-FunctionAttr *Builder::getFunctionAttr(Function *value) {
+FunctionAttr *Builder::getFunctionAttr(const Function *value) {
   return FunctionAttr::get(value, context);
 }