Why does stat(2) say <unistd.h> is needed?

[Jonathan Wakely <jwakely@redhat.com>]

The stat(2) man page says:

SYNOPSIS
        #include <sys/types.h>
        #include <sys/stat.h>
        #include <unistd.h>

        int stat(const char *pathname, struct stat *statbuf);
        int fstat(int fd, struct stat *statbuf);
        int lstat(const char *pathname, struct stat *statbuf);

But I don't see anything there that would require <unistd.h>. POSIX
doesn't require it (and since POSIX.1-2001 no longer requires
<sys/types.h>, saying "Although <sys/types.h> was required for
conforming implementations of previous POSIX specifications, it was
not required for UNIX applications.")

Is the inclusion of <unistd.h> there a mistake?

I've been trying to track down why a libstdc++ header includes
<unistd.h> for no apparent reason, and my best guess is that it's a
result of this man page saying to do it.