FindLua.cmake is a copy from the cmake repo:
0419ecbcad/Modules/FindLua.cmake.
It's a cmake module, meaning it's already shipped with cmake by default.
There have been two changes done to our version of FindLua.cmake.
The first change is that
include(${CMAKE_CURRENT_LIST_DIR}/FindPackageHandleStandardArgs.cmake)
was changed to
include(FindPackageHandleStandardArgs.cmake)
This change is required only because we have imported FindLua.cmake
module but not FindPackageHandleStandardArgs module. Had FindLua been
called as a module as intended then this file would not need changing.
The second change is that support for Lua 5.4 is added. However, support
for any version of Lua except for 5.1 is disabled since
e322b5c864.
Because these changes from the upstream FindLua.cmake is unnecessary I
believe we can and should use the builtin FindLua.cmake instead of our
own.