The syscall __NR_pselect6_time64 (32-bit) or __NR_pselect6 (64-bit)
is used as default. For architectures with __ASSUME_TIME64_SYSCALLS
the 32-bit fallback uses __NR_pselec6.
To accomodate microblaze missing pselect6 support on kernel older
than 3.15 the fallback is moved to its own function to the microblaze
specific implementation can override it.
Checked on x86_64-linux-gnu and i686-linux-gnu (on 5.4 and on 4.15
kernel).
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
