Use a DepNode for the generator signature

src/librustc/dep_graph/dep_node.rs

@@ -432,6 +432,7 @@ define_dep_nodes!( <'tcx>
     [] ImplPolarity(DefId),
     [] ClosureKind(DefId),
     [] FnSignature(DefId),
+    [] GenSignature(DefId),
     [] CoerceUnsizedInfo(DefId),
 
     [] ItemVarianceConstraints(DefId),

src/librustc/ty/maps.rs

@@ -919,7 +919,7 @@ define_maps! { <'tcx>
 
     /// Records the signature of each generator. The def ID is the ID of the
     /// expression defining the closure.
-    [] generator_sig: TypeckTables(DefId) -> Option<ty::PolyGenSig<'tcx>>,
+    [] generator_sig: GenSignature(DefId) -> Option<ty::PolyGenSig<'tcx>>,
 
     /// Caches CoerceUnsized kinds for impls on custom types.
     [] coerce_unsized_info: CoerceUnsizedInfo(DefId)