Add #include required on win32.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@41686 91177308-0d34-0410-b5e6-96231b3b80d8

Lex/Preprocessor.cpp

@@ -38,6 +38,7 @@
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include <iostream>
+#include <ctime>
 using namespace clang;
 
 //===----------------------------------------------------------------------===//