[C++11] More 'nullptr' conversion or in some cases just using a boolean check instead of comparing to nullptr.

llvm-svn: 206129
diff --git a/llvm/lib/MC/SubtargetFeature.cpp b/llvm/lib/MC/SubtargetFeature.cpp
index 2fb91f2..2ce7d1b 100644
--- a/llvm/lib/MC/SubtargetFeature.cpp
+++ b/llvm/lib/MC/SubtargetFeature.cpp
@@ -126,7 +126,7 @@
   // Binary search the array
   const SubtargetFeatureKV *F = std::lower_bound(A, Hi, S);
   // If not found then return NULL
-  if (F == Hi || StringRef(F->Key) != S) return NULL;
+  if (F == Hi || StringRef(F->Key) != S) return nullptr;
   // Return the found array item
   return F;
 }