Linux: consolidate sendfile implementation

This is similar to other LFS consolidation, where the non-LFS is only
built if __OFF_T_MATCHES_OFF64_T is not defined and the LFS version
is aliased to non-LFS name if __OFF_T_MATCHES_OFF64_T is defined.

For non-LFS variant, use sendfile syscall if defined, otherwise use
sendfile64 plus the offset overflow check (as generic implementation).

Checked on x86_64-linux-gnu.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Tested-by: Carlos O'Donell <carlos@redhat.com>

sysdeps/unix/sysv/linux/sendfile64.c

@@ -0,0 +1,37 @@
+/* Transfer data between file descriptors.  Linux version.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library.  If not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <sys/sendfile.h>
+#include <stddef.h>
+#include <errno.h>
+#include <sysdep.h>
+
+/* Send COUNT bytes from file associated with IN_FD starting at OFFSET to
+   descriptor OUT_FD.  */
+ssize_t
+sendfile64 (int out_fd, int in_fd, off64_t *offset, size_t count)
+{
+#ifndef __NR_sendfile64
+# define __NR_sendfile64 __NR_sendfile
+#endif
+  return INLINE_SYSCALL_CALL (sendfile64, out_fd, in_fd, offset, count);
+}
+
+#ifdef __OFF_T_MATCHES_OFF64_T
+strong_alias (sendfile64, sendfile)
+#endif