tools: fix luacheck invocation in different cases

Now `make luacheck` gracefully handles different cases[^1]: in-source
and out-of-source build (within the source tree or outside), current
working directory as a real path or with symlink components.

As result of looking into those problems I filed the issue [1] against
luacheck. It seems, there are problems around absolute paths with
symlinks components.

[^1]: We have the similar problems with LuaJIT's luacheck rule. They
      will be fixed in a separate patch.

[1]: https://github.com/mpeterv/luacheck/issues/208



Reviewed-by: Sergey Bronnikov <sergeyb@tarantool.org>
Reviewed-by: Igor Munkin <imun@tarantool.org>