Xmir crashes immediately on arm64

I don't have any arm64 hardware myself but I can tell what the problem is already.

Fixed at:
https://git.launchpad.net/~xmir-team/xorg-server/+git/xmir/commit/?id=ca0952d8837f752186a9b6e55e534eac78bbbb18

This bug was fixed in the package xorg-server - 2:1.19.3-1ubuntu1

---------------
xorg-server (2:1.19.3-1ubuntu1) zesty; urgency=medium

  [ Timo Aaltonen ]
  * Merge from Debian experimental. (LP: #1671799)
    - Patches refreshed
    - randr-adjust-masters-last-set-time.diff,
      modesetting-unifdef-slave-support.diff: Dropped, upstream
    - config-add-no-removal.patch, xf86-inactive-gpuscreen.patch,
      fix-detach-gpu.patch: Dropped, more or less obsolete
  * 190_cache-xkbcomp_output_for_fast_start_up.patch: Cleaned up from
    the package as it wasn't used.
  * 111_armel-drv-fallbacks.patch: Dropped, we don't ship these drivers
    anymore.
  * rules: Drop the workaround that adds lt_cv_prog_compiler_static_works=no
    to confflags.
  * 232-xf86compatoutput-valgrind.patch: This was added upstream
    already, no need to carry a duplicate check.
  * 208_switch_on_release.diff: Dropped, doesn't work with 1.19.
  * 228_autobind_gpu.patch: Update from Fedora, fixes nvidia.
  * disable-rotation-transform-gpuscreens.patch: Dropped, nvidia
    supports rotation now.
  * 122_xext_fix_card32_overflow_in_xauth.patch: Dropped, upstream
    review found issues and it never got applied.
  * xfree86-no-xv-for-gpuscreens.patch: Drop bogus buglink.
  * 227_null_ptr_midispcur.patch: Dropped, upstream didn't accept it.
  * randr-do-not-check-the-screen-size.diff: Dropped, can't reproduce
    #1586260 anymore without the patch.

  [ Robert Ancell ]
  * debian/patches/xmir.patch:
    - Refresh
    - Fix warnings when built against lp:mir/0.25
    - Support both Mir 0.24, 0.25 and 0.26 client APIs
    - Fix crashing on arm64 (LP: #1642297)

xorg-server (2:1.19.3-1) unstable; urgency=medium

  * New upstream release.

xorg-server (2:1.19.2-1) unstable; urgency=medium

  [ Andreas Boll ]
  * xserver-xorg-core.bug.script: Change udevadm path from /sbin to /bin
    (Closes: #852584).

  [ Emilio Pozuelo Monfort ]
  * New upstream stable release.
    - CVE-2017-2624: Timing attack against MIT cookie. Closes: #856398.
  * control: Build-depend on libbsd-dev everywhere, needed for
    arc4random_buf for the above fix.

xorg-server (2:1.19.1-4) unstable; urgency=medium

  * rules: Only set the suid bit on Xorg.wrap when building arch:any
    packages. Thanks Julien Cristau.

xorg-server (2:1.19.1-3) unstable; urgency=medium

  * rules: Fix setting suid bit on Xorg.wrap.
  * rules: Don't ignore errors when setting the suid bit.

xorg-server (2:1.19.1-2) unstable; urgency=medium

  * rules: Fix udeb regression from dh migration. Should also fix FTBFS
    on hurd and kfreebsd.
  * rules: Add --fail-missing to dh_install.
  * rules: Remove unused vars config_backend_main and
    config_backend_udeb.

xorg-server (2:1.19.1-1) unstable; urgency=medium

  [ Emilio Pozuelo Monfort ]
  * Switch to dh.
  * Drop build-deps on automake and libtool, dh-autoreconf depends on
    them for us.
  * rules: use install consistently.
  * Drop pre-wheezy Breaks.

  [ Andreas Boll ]
  * New upstream release.
    - AttendClient of grab-pervious client must queue to
      saved_ready_clients [v2] (Closes: #846779, #850940).
    - present: Only call present_flip_notify if vblank->queu...