Add some missing includes for the build against stdcxx.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161657 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/TableGen/StringToOffsetTable.h b/utils/TableGen/StringToOffsetTable.h
index 803f5bd..a098d7d 100644
--- a/utils/TableGen/StringToOffsetTable.h
+++ b/utils/TableGen/StringToOffsetTable.h
@@ -14,6 +14,7 @@
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/raw_ostream.h"
+#include <cctype>
 
 namespace llvm {