Add include missing for VC build.

llvm-svn: 111484
diff --git a/llvm/utils/TableGen/ClangAttrEmitter.cpp b/llvm/utils/TableGen/ClangAttrEmitter.cpp
index 463f684..c773e57f 100644
--- a/llvm/utils/TableGen/ClangAttrEmitter.cpp
+++ b/llvm/utils/TableGen/ClangAttrEmitter.cpp
@@ -15,6 +15,7 @@
 #include "Record.h"
 #include "llvm/ADT/StringSwitch.h"
 #include <algorithm>
+#include <cctype>
 
 using namespace llvm;