libbpf-tools: determine target host architecture
libbpf-tools: determine target host architecture

BPF code is compiled with -target bpf, but for PT_REGS_PARM macro (and by
induction for BPF_KPROBE/BPF_KRETPROBE macros as well), it's important to know
what's the target host original architecture was, to use correct definition of
struct pt_regs. Determine that based on output of `uname -m` (taking into
account that both x86_64 and x86 are defined as x86 internally for kernel).

Signed-off-by: Andrii Nakryiko <1ab6096f60c2d8d3f6ff85bf25d0ee81fb25b434@fb.com>

tuxology/bcc,brendangregg/bcc,tuxology/bcc,iovisor/bcc,brendangregg/bcc,tuxology/bcc,iovisor/bcc,brendangregg/bcc,tuxology/bcc,iovisor/bcc,brendangregg/bcc,iovisor/bcc,brendangregg/bcc,iovisor/bcc,tuxology/bcc