Add a forward decl, oops.

llvm-svn: 573
diff --git a/llvm/lib/CodeGen/InstrSched/SchedGraph.h b/llvm/lib/CodeGen/InstrSched/SchedGraph.h
index e12d90f..35cdfd2 100644
--- a/llvm/lib/CodeGen/InstrSched/SchedGraph.h
+++ b/llvm/lib/CodeGen/InstrSched/SchedGraph.h
@@ -33,6 +33,7 @@
 class SchedGraphNode; 
 class SchedGraph; 
 class NodeToRegRefMap;
+class MachineInstr;
 
 /******************** Exported Data Types and Constants ********************/