lua: fix build issue with gcc 4.6

gcc 4.6 has become more sensitive about option ordering, especially
libraries. It requires the -l flags to be placed after the object
files that need that library. See for example
http://nick.zoic.org/art/etc/gcc-linker-libs.html

. We had -llua at the
beginning of the link command line, causing build issues (here on gcc
4.6 with host-lua).

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>