Add include missing for VC build.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111484 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/TableGen/ClangAttrEmitter.cpp b/utils/TableGen/ClangAttrEmitter.cpp
index 463f684..c773e57 100644
--- a/utils/TableGen/ClangAttrEmitter.cpp
+++ b/utils/TableGen/ClangAttrEmitter.cpp
@@ -15,6 +15,7 @@
 #include "Record.h"
 #include "llvm/ADT/StringSwitch.h"
 #include <algorithm>
+#include <cctype>
 
 using namespace llvm;