[vm] Repair interpreter build.

Change-Id: I194b705523cec3ebb1c3edba6546561c337b28c9
Reviewed-on: https://dart-review.googlesource.com/58600
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>
diff --git a/runtime/vm/compiler/frontend/kernel_binary_flowgraph.cc b/runtime/vm/compiler/frontend/kernel_binary_flowgraph.cc
index cd27d7b..c799b2e 100644
--- a/runtime/vm/compiler/frontend/kernel_binary_flowgraph.cc
+++ b/runtime/vm/compiler/frontend/kernel_binary_flowgraph.cc
@@ -1269,6 +1269,8 @@
         closure.SetParameterNameAt(pos, Symbols::ClosureParameter());
         pos++;
 
+        const Library& lib = Library::Handle(
+            builder_->zone_, builder_->active_class()->klass->library());
         for (intptr_t j = 0; j < positional_parameter_count; ++j, ++pos) {
           VariableDeclarationHelper helper(builder_);
           helper.ReadUntilExcluding(VariableDeclarationHelper::kType);