[buck] always create multilinks for attribute files

Summary:
The only path to the `MergeCaptured.slink` function is when we should merge, so
it doesn't make sense to check `Config.merge` again. In the case of `infer run
--flavors -- buck ...`, this would create regular symlinks instead of the much
faster multilinks.

Reviewed By: jberdine

Differential Revision: D5574020

fbshipit-source-id: df710ca

infer/src/backend/mergeCapture.ml

@@ -101,7 +101,7 @@ let rec slink ~stats ~skiplevels src dst =
           (Filename.concat dst item))
       items )
   else if skiplevels > 0 then ()
-  else if Config.merge && Filename.check_suffix dst ".attr" then add_multilink_attr ~stats src dst
+  else if Filename.check_suffix dst ".attr" then add_multilink_attr ~stats src dst
   else create_link ~stats src dst
 
 (** Determine if the destination should link to the source.

infer/src/integration/Driver.ml

@@ -180,9 +180,7 @@ let clean_results_dir () =
 
 let check_captured_empty mode =
   let clean_command_opt = clean_compilation_command mode in
-  (* if merge is passed, the captured folder will be empty at this point,
+  if Utils.directory_is_empty Config.captured_dir then (
-     but will be filled later on. *)
-  if Utils.directory_is_empty Config.captured_dir && not Config.merge then (
     ( match clean_command_opt with
     | Some clean_command
      -> L.user_warning "@\nNothing to compile. Try running `%s` first.@." clean_command