Silence dead store warning.  It is conceptually possible we will
add more code that references SourceFile, so removing the dead store
doesn't seem appropriate for the long term.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@165837 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Basic/SourceManager.cpp b/lib/Basic/SourceManager.cpp
index 65bd601..eefaacc 100644
--- a/lib/Basic/SourceManager.cpp
+++ b/lib/Basic/SourceManager.cpp
@@ -1577,6 +1577,7 @@
     }      
   }
   
+  (void) SourceFile;
   return FirstFID;
 }