Before this change rclone used statx() to read the metadata for files
from the local filesystem when `-M` was in use.
Unfortunately statx() was only introduced in kernel 4.11 which was
released in April 2017 so there are current systems (eg Centos 7)
still on kernel versions which don't support statx().
This patch checks to see if statx() is available and if it isn't, it
falls back to using fstatat() which was introduced in Linux 2.6.16
which is guaranteed for all Go versions.
See: https://forum.rclone.org/t/metadata-from-linux-local-s3-failed-to-copy-failed-to-read-metadata-from-source-object-function-not-implemented/33233/
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