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

llvm-svn: 206142
diff --git a/llvm/lib/CodeGen/GCMetadata.cpp b/llvm/lib/CodeGen/GCMetadata.cpp
index 54b047b..c47450e 100644
--- a/llvm/lib/CodeGen/GCMetadata.cpp
+++ b/llvm/lib/CodeGen/GCMetadata.cpp
@@ -84,7 +84,7 @@
   }
  
   dbgs() << "unsupported GC: " << Name << "\n";
-  llvm_unreachable(0);
+  llvm_unreachable(nullptr);
 }
 
 GCFunctionInfo &GCModuleInfo::getFunctionInfo(const Function &F) {