[C++11] Make use of 'nullptr' in the Support library.

llvm-svn: 205697
diff --git a/llvm/lib/Support/Regex.cpp b/llvm/lib/Support/Regex.cpp
index 1115534..f7fe1e4 100644
--- a/llvm/lib/Support/Regex.cpp
+++ b/llvm/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);