[php-doctrine-orm/f21] Ensure 512M of memory (instead of default 128M) so mock x86_64 builds pass (BZ #1159650)

[Shawn Iwinski]

Summary of changes:

  583768c... Ensure 512M of memory (instead of default 128M) so mock x86 (*)

(*) This commit already existed in another branch; no separate mail sent