sysdeps/posix/{pread64,pwrite64}.c

[Roland McGrath <roland at frob dot com>]

I think these are bogus, for several reasons.  They have been there for a
while, but I just noticed because they just started breaking things (I
guess something else is calling them).

Firstly, sysdeps/posix is for functions implemented in terms of POSIX entry
points.  lseek64 is not a POSIX entry point, so a function using it has no
business residing in sysdeps/posix.  

Secondly (and this is a problem with sysdeps/posix/{pread,pwrite}.c too),
the whole point of pread/pwrite is to be thread-safe as opposed to using
lseek.  I think it is dangerously misleading to provide an incorrect
implementation instead of none at all.  If a threaded program wants to use
file descriptors safely, it needs to know that pread/pwrite work as
specified or else that it must do its own synchronization.  In the current
situation, one will believe there is a pread/pwrite but in fact the
specified functionality is not available.