[design change] record-replay linux ABI level

[Tom Tromey]

Oza> The definition of system call record maps fine to x86.  but arm
Oza> syscall numbers are different. [partially] for e.g. on x86 sycall
Oza> number for sys_epoll_create = 254 while on ARM it is 250.  the more
Oza> we go down on defined system calls the more the numbers are
Oza> differing on ARM and we loose one to one trivial mapping.

My understanding of the current design is that the ARM code would see
the syscall 250, and have a mapping to turn that into
gdb_sys_epoll_create (== 254).  This can be done bidirectionally with
two lookup tables.

I suppose this could still not work in some scenarios.  One question is
whether these occur in practice or are merely theoretical.

I don't really care about this API either way.
With a solid justification it is fine to change it.

Tom