lang/luajit-openresty: fix build on powerpc64 elfv2

lua_assert is undefined, which makes build fail with:
/usr/local/bin/ld: libluajit.a(lj_ccallback.o): in function `lj_ccallback_new':
lj_ccallback.c:(.text+0xbc8): undefined reference to `lua_assert'

lua_assert is defined in lualib.h.