[ASTMatchers] work around a miscompile; "NFC"

I chatted with Reid offline, and we agreed that having a workaround here
would be appropriate until PR43879 is resolved.

The given transformation Works On My Machine(TM), and should hopefully
hold more broadly, but my fingers are crossed nonetheless. :)

clang/lib/ASTMatchers/ASTMatchFinder.cpp

@@ -904,8 +904,9 @@ bool MatchASTVisitor::objcClassIsDerivedFrom(
     if (Base.matches(*ClassDecl, this, Builder))
       return true;
 
+    // Not `return false` as a temporary workaround for PR43879.
     if (Directly)
-      return false;
+      break;
   }
 
   return false;