testbuild target is broken for Tor Browser 64 bit (versionCode can't get computed)

0:03.87 Traceback (most recent call last):
0:03.87   File "/usr/lib/python2.7/runpy.py", line 174, in _run_module_as_main
0:03.88     "__main__", fname, loader, pkg_name)
0:03.88   File "/usr/lib/python2.7/runpy.py", line 72, in _run_code
0:03.88     exec code in run_globals
0:03.88   File "/var/tmp/build/firefox-4516c5951e84/python/mozbuild/mozbuild/action/file_generate.py", line 120, in <module>
0:03.88     sys.exit(main(sys.argv[1:]))
0:03.88   File "/var/tmp/build/firefox-4516c5951e84/python/mozbuild/mozbuild/action/file_generate.py", line 71, in main
0:03.88     ret = module.__dict__[method](output, *args.additional_arguments, **kwargs)
0:03.88   File "/var/tmp/build/firefox-4516c5951e84/mobile/android/base/generate_build_config.py", line 145, in generate_android_manifest
0:03.88     defines=_defines(),
0:03.88   File "/var/tmp/build/firefox-4516c5951e84/mobile/android/base/generate_build_config.py", line 129, in _defines
0:03.88     max_sdk=max_sdk)
0:03.88   File "/var/tmp/build/firefox-4516c5951e84/python/mozbuild/mozbuild/android_version_code.py", line 140, in android_version_code
0:03.88     return android_version_code_v0(buildid, *args, **kwargs)
0:03.88   File "/var/tmp/build/firefox-4516c5951e84/python/mozbuild/mozbuild/android_version_code.py", line 31, in android_version_code_v0
0:03.88     "for CPU arch %s" % cpu_arch)
0:03.88 ValueError: Don't know how to compute android:versionCode for CPU arch arm64-v8a

I think this will be fixed once we move away from ESR 68 as I've been doing test builds for legacy/trac#33626 (moved). Still, even if so, this is a bug in our current setup.