editors/pragtical: fix build on powerpc*

1. On powerpc:

../src/api/utf8.c:854:22: error: use of undeclared identifier 'INT_MAX'

854 |   if (pose - posi >= INT_MAX)  /* (lua_Integer -> int) overflow? */
    |                      ^

2. Also set USES=luajit to use luajit-openresty on powerpc64*.