Fix include path of libxdp for each arch

[ami-GS]

Fix of #4
Doesn't need to install gcc-multilib anymore nor set sympath as ln -s /usr/include/x86_64-linux-gnu/asm /usr/include/asm

[tohojo]

Including arch-specific headers in a BPF program should not be needed; what error are you seeing that this fixes, exactly?

[ami-GS]

This is the error. This doesn't happen with gcc-multilib or my change

root@861ec1d9b02c:~/msquic/submodules/xdp-tools# make

lib

libbpf
CC libbpf/src/libbpf.a
INSTALL libbpf/src/libbpf.a

libxdp
CC staticobjs/libxdp.o
CC staticobjs/xsk.o
M4 xdp-dispatcher.c
CLANG xdp-dispatcher.o
In file included from xdp-dispatcher.c:3:
In file included from ../../headers/linux/bpf.h:11:
/usr/include/linux/types.h:5:10: fatal error: 'asm/types.h' file not found
#include <asm/types.h>
^~~~~~~~~~~~~
1 error generated.
make[2]: *** [Makefile:137: xdp-dispatcher.o] Error 1
make[1]: *** [Makefile:20: libxdp] Error 2
make: *** [Makefile:25: lib] Error 2

[tohojo]

Hmm, okay, seems we do indeed use the arch includes for the uXX definitions. I wonder if that works correctly when compiling on a 32-bit arch? Anyway, I don't suppose there's anything wrong with fixing it this way, then :)