* amd64-nat.h (amd64_native_gregset_supplies_p): Add gdbarch as
parameter.
* amd64-nat.c (amd64_native_gregset_supplies_p): Likewise.
(amd64_native_gregset_reg_offset): Add gdbarch as parameter. Replace
current_gdbarch by gdbarch. Update caller.
* amd64-linux-nat.c (amd64_linux_fetch_inferior_registers)
(amd64_linux_store_inferior_registers): Use get_regcache_arch to get at
the current architecture. Update calls of
amd64_native_gregset_supplies_p.
* amd64bsd-nat.c (amd64bsd_fetch_inferior_registers)
(amd64bsd_store_inferior_registers): Likewise.