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

llvm-svn: 205697
diff --git a/llvm/lib/Support/Path.cpp b/llvm/lib/Support/Path.cpp
index 5b73631..d345829 100644
--- a/llvm/lib/Support/Path.cpp
+++ b/llvm/lib/Support/Path.cpp
@@ -577,7 +577,7 @@
   // macros defined in <unistd.h> on darwin >= 9
   int ConfName = erasedOnReboot? _CS_DARWIN_USER_TEMP_DIR
                                : _CS_DARWIN_USER_CACHE_DIR;
-  size_t ConfLen = confstr(ConfName, 0, 0);
+  size_t ConfLen = confstr(ConfName, nullptr, 0);
   if (ConfLen > 0) {
     do {
       result.resize(ConfLen);