syscall, internal/syscall: adjust use of largefile functions

Consistently call __go_openat for openat.  Use fstatat64, creat64,
sendfile64, and getdents64 where needed.

Based on patch by Rainer Orth.

Fixes https://gcc.gnu.org/PR89447

Change-Id: I5c7e9144c6239a969eb561997ef6d5931d984d1a
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/166420
Reviewed-by: Ian Lance Taylor <iant@golang.org>
11 files changed