[llvm][StringExtras] Add missing include of cctype

This fixes build breakages on windows.

llvm/lib/Support/StringExtras.cpp

@@ -13,6 +13,8 @@
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/raw_ostream.h"
+#include <cctype>
+
 using namespace llvm;
 
 /// StrInStrNoCase - Portable version of strcasestr.  Locates the first