main/luajit: switch to OpenResty's maintained branch

The MoonJIT fork is unmaintained since September 2020 [1]:

> This code base does not have an active maintainer anymore, please
> read this [Twitter thread][2] to know more. If you are an existing
> contributor (or otherwise have an interest in maintaining this
> project actively) then please email me using the email address in
> my Twitter profile.

Moreover, the transition from original LuaJIT to MoonJIT caused multiple
compatibility and stability issues, mainly with Lua NGINX module
(#12410, #10478), but also with some Lua packages written in C (segfaults).

I wanted to switch back to the original (Mike's) LuaJIT, the latest revision
from the v2.1 branch. The problem is that it doesn't support ppc64le and
s390x. The existing patches don't apply anymore and I really don't have
enough knowledge and insanity in blood to update them. Dropping these
architectures would require updating many dependent aports which is not
a good idea at this moment (v3.14 will be released very soon).

OpenResty's "fork" seems to be the only active LuaJIT fork that regularly
synchronize changes from the upstream LuaJIT project and provides support
for all architectures we need.

> This is the official OpenResty branch of LuaJIT. It is not to be
> considered a fork, since we still regularly synchronize changes from the
> upstream LuaJIT project

Patches CVE-2020-15890 and 20-src-lib_string are already included in the
OpenResty's branch.

[1]: https://github.com/moonjit/moonjit/commit/a2a39ea7184f3c8cab9474c6e41f6541265fb362:
[2]: https://twitter.com/siddhesh_p/status/1308594269502885889

Resolves #12410 #10478
8 jobs for !22273 with luajit-openresty in 2 minutes and 12 seconds (queued for 1 second)
latest detached
Status Job ID Name Coverage
  Lint
failed #413476
docker-alpine x86_64 allowed to fail
lint

00:00:21

 
  Build
canceled #413481
docker-alpine ci-build aarch64
build-aarch64

canceled #413483
docker-alpine ci-build armhf
build-armhf

canceled #413482
docker-alpine ci-build armv7
build-armv7

canceled #413480
docker-alpine ci-build ppc64le
build-ppc64le

passed #413479
docker-alpine ci-build s390x
build-s390x

00:01:03

passed #413478
docker-alpine ci-build x86
build-x86

00:00:26

passed #413477
docker-alpine ci-build x86_64
build-x86_64

00:00:21

 
Name Stage Failure
failed
lint Lint
No job log