The "Attribute Meanings" and "File Times" nodes describe microsecond
st_atime_usec etc fields for the stat structure, but it seems they're
not provided on a gnu/linux system (judging by the little program
below failing to compile).

It'd be good if those bits of description could be qualified as gnu
extensions, or hurd-specific, or hurd plus bsd, or whatever, so you
know not to expect them always available.