Remove some stray uses of <ctype.h> functions.

These are causing assertions on some MSVC builds.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174805 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Lex/HeaderMap.cpp b/lib/Lex/HeaderMap.cpp
index 9be7b03..dcf1f0c 100644
--- a/lib/Lex/HeaderMap.cpp
+++ b/lib/Lex/HeaderMap.cpp
@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "clang/Lex/HeaderMap.h"
+#include "clang/Basic/CharInfo.h"
 #include "clang/Basic/FileManager.h"
 #include "llvm/ADT/OwningPtr.h"
 #include "llvm/ADT/SmallString.h"
@@ -61,7 +62,7 @@
   const char *S = Str.begin(), *End = Str.end();
 
   for (; S != End; S++)
-    Result += tolower(*S) * 13;
+    Result += toLowercase(*S) * 13;
   return Result;
 }