main/lua-sql: Fix CFLAGS for Lua 5.2 and greater
The newer versions of Lua were being built with the CFLAGS for all earlier versions of Lua, plus its own. So, lua5.4-sql was being built with the include files for Lua 5.2, 5.3, and 5.4. This broke support for the lua_newuserdata macro, among others.