Unbreak build.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@66874 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/TableGen/TGSourceMgr.h b/utils/TableGen/TGSourceMgr.h
index 9a61a9b..33d3c10 100644
--- a/utils/TableGen/TGSourceMgr.h
+++ b/utils/TableGen/TGSourceMgr.h
@@ -14,6 +14,7 @@
 #ifndef TGSOURCEMGR_H
 #define TGSOURCEMGR_H
 
+#include <cassert>
 #include <vector>
 
 namespace llvm {