[Tarantool-patches] [PATCH] Remove hardcoded paths to LuaJIT tests

[Igor Munkin]

As a result of the review[1] for Timur patch, I've finally got the idea
how to reduce the struggling Kirill faces every time there is a new test
created within LuaJIT third party repo. The series contains of two
patches in both repos:
* the root CMakeLists.txt for test directory is introduced to LuaJIT
  repo in scope of the first patch
* the paths in test/CMakeLists.txt are accordingly adjusted

Issue: https://github.com/tarantool/tarantool/issues/5425
LuaJIT repo branches:
* https://github.com/tarantool/luajit/tree/imun/gh-5425-luajit-tests-cmake
* https://github.com/tarantool/luajit/tree/imun/gh-5425-luajit-tests-cmake-2.5
Tarantool repo branch (need to be cherry-picked to all stable branches):
* https://github.com/tarantool/tarantool/tree/imun/gh-5425-luajit-tests-cmake

CI is not green, but I've done my best. I see neither build fails nor
failures related to the luajit-tap tests here:
* https://gitlab.com/tarantool/tarantool/-/pipelines/203537445

[1]: https://lists.tarantool.org/pipermail/tarantool-patches/2020-October/020266.html

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2.25.0