[merge] attach dbs immutably

Summary: When merging buck-out outputs, use the `immutable` flag. This prevents SQLite from writing to these databases, or to create intermediate files (like the writeahead log) in buck-out.

Reviewed By: jvillard

Differential Revision:
D46836978

Privacy Context Container: L1122176

fbshipit-source-id: 35933104e398d723014002321934a20f50a33648

infer/src/base/DBWriter.ml

@@ -141,7 +141,8 @@ module Implementation = struct
       if not (ISys.file_exists db_file) then
         L.die InternalError "Tried to merge in DB at %s but path does not exist.@\n" db_file ;
       let main_db = Database.get_database CaptureDatabase in
-      SqliteUtils.with_attached_db main_db ~db_file ~db_name:"attached" ~f:(fun () ->
+      SqliteUtils.with_attached_db main_db ~db_file ~db_name:"attached" ~immutable:true
+        ~f:(fun () ->
           merge_procedures_table ~db:CaptureDatabase ~to_db:"memdb" ~db_file ;
           merge_source_files_table ~db_file )
     in