python_examples/getifaddrs_ctypes: use SIOCGIFINDEX to retrieve interface index

This commit also integrates little fixes for systems with several IP4
addresses per interface (eg. "eth0:0" interface) and with L3 interfaces
(eg. "tun0").
python_examples/getifaddrs_ctypes: increase sll_halen to support IP6IP6 tunnel interfaces

Such interface:

* are named like "ip6tnl0" with old udev rules,
* have sll_hatype = ARPHRD_TUNNEL6
* are presented "link/tunnel6" by "ip addr"
nolibc: fix -m32 detection on systems missing 32bits headers
mbr/syslinux-mbr: add *.o files to .PRECIOUS target to prevent them from being removed