Add some missing includes for the build against stdcxx.

llvm-svn: 161657
diff --git a/llvm/utils/TableGen/StringToOffsetTable.h b/llvm/utils/TableGen/StringToOffsetTable.h
index 803f5bd..a098d7d 100644
--- a/llvm/utils/TableGen/StringToOffsetTable.h
+++ b/llvm/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 {