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

llvm-svn: 205829
diff --git a/llvm/lib/Support/SourceMgr.cpp b/llvm/lib/Support/SourceMgr.cpp
index 4aa6ff7..ca68289 100644
--- a/llvm/lib/Support/SourceMgr.cpp
+++ b/llvm/lib/Support/SourceMgr.cpp
@@ -114,7 +114,7 @@
     if (*Ptr == '\n') ++LineNo;
 
   // Allocate the line number cache if it doesn't exist.
-  if (LineNoCache == nullptr)
+  if (!LineNoCache)
     LineNoCache = new LineNoCacheTy();
 
   // Update the line # cache.