linux(4): Add AT_NO_AUTOMOUNT to statx.

Specific to Linux AT_NO_AUTOMOUNT flag tells the kernel to not automount the
terminal component of pathname if it is a directory that is an automount point.
As it is the default for FreeBSD silencly ignore this flag.

glibc-2.34 uses this flag in the stat64 system calls which is used by i386.

Reviewed by: trasz
Differential revision: https://reviews.freebsd.org/D31524
MFC after: 2 weeks