[C++11] Replace some comparisons with 'nullptr' with simple boolean checks to reduce verbosity.

llvm-svn: 205829
diff --git a/llvm/lib/Support/PrettyStackTrace.cpp b/llvm/lib/Support/PrettyStackTrace.cpp
index aef02e9..987778a 100644
--- a/llvm/lib/Support/PrettyStackTrace.cpp
+++ b/llvm/lib/Support/PrettyStackTrace.cpp
@@ -46,7 +46,7 @@
 /// PrintCurStackTrace - Print the current stack trace to the specified stream.
 static void PrintCurStackTrace(raw_ostream &OS) {
   // Don't print an empty trace.
-  if (PrettyStackTraceHead->get() == nullptr) return;
+  if (!PrettyStackTraceHead->get()) return;
   
   // If there are pretty stack frames registered, walk and emit them.
   OS << "Stack dump:\n";