Update LLVM for 3.5 rebase (r209712).

Change-Id: I149556c940fb7dc92d075273c87ff584f400941f
diff --git a/lib/Support/Regex.cpp b/lib/Support/Regex.cpp
index 1115534..f7fe1e4 100644
--- a/lib/Support/Regex.cpp
+++ b/lib/Support/Regex.cpp
@@ -43,7 +43,7 @@
   if (!error)
     return true;
   
-  size_t len = llvm_regerror(error, preg, NULL, 0);
+  size_t len = llvm_regerror(error, preg, nullptr, 0);
   
   Error.resize(len - 1);
   llvm_regerror(error, preg, &Error[0], len);