x86: Hook up pread64 in 32/64 bit linux, and pwrite64 in 32 bit.

x86: Hook up pread64 in 32/64 bit linux, and pwrite64 in 32 bit.

My new computer has a dynamic linker which seems to use the pread64
system call, and since that gets pulled in when running tests, that
needs to be implemented for tests to pass on that machine, making it
possible to detect problems the failure might ohterwise mask.

This is only really necessary for 64 bit linux, but while I'm here I
hooked it up for 32 bit linux as well. I also added pwrite64 for 32 bit
linux since that was only enabled for 64 bit.

Change-Id: I8d2061d30e98a1581c5e30b522b6ba12aea20ecd
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/26604
Reviewed-by: Matthew Poremba <matthew.poremba@amd.com>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>