[analyzer] Rename addTrackNullOrUndefValueVisitor to trackNullOrUndefValue.

This helper function (in the clang::ento::bugreporter namespace) may add more
than one visitor, but conceptually it's tracking a single use of a null or
undefined value and should do so as best it can.

Also, the BugReport parameter has been made a reference to underscore that
it is non-optional.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@162720 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/StaticAnalyzer/Checkers/UnixAPIChecker.cpp b/lib/StaticAnalyzer/Checkers/UnixAPIChecker.cpp
index d35455c..d298dd9 100644
--- a/lib/StaticAnalyzer/Checkers/UnixAPIChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/UnixAPIChecker.cpp
@@ -224,7 +224,7 @@
   BugReport *report = new BugReport(*BT_mallocZero, os.str(), N);
 
   report->addRange(arg->getSourceRange());
-  bugreporter::addTrackNullOrUndefValueVisitor(N, arg, report);
+  bugreporter::trackNullOrUndefValue(N, arg, *report);
   C.EmitReport(report);
 
   return true;