Allow multiple architecture syscall_num.stp files to be used by bpf backend

Allow multiple architecture syscall_num.stp files to be used by bpf backend

Systemtap's BPF still has the concept of target architecture and isn't
write once run anywhere for BPF code.  Thus, to make the syscall_any
tapset work the tapset needs to have all the different architecture
initialization code available and select the appropriate one based on
the architecture.  Thus, each syscalls_num.stp file has preprocessing
guards to make them empty unless the architecture matches.