BuildSystem: Enable Lua 5.4.

Note to maintainers: Lua 5.4, Lua 5.3, and Lua 5.2 have not been tested
at runtime with pbx_lua. Until then, use the lowest available version
of Lua, if you enabled the module pbx_lua at all.

Change-Id: Ie5270448b11fcb4e2a53d899e4fe7fea793ce7e0