Changeset b4e3b2b in rtems for c/src/wrapup

Patch from Ian Lance Taylor <ian@…>.

I just happened across the sync_io support in

c/src/exec/score/cpu/unix/cpu.c

(is this documented anywhere?). That looked more useful than the
signal driven I/O I was using before, so I tried it. I ran across a
few bugs in the way it uses select.

Select changes its fd_set arguments, so you can't use global variables
for them. You have to copy them into local variables first.

If select returns -1 with errno set to EINTR, then it has not changed
any of the fd_sets. You can't start looking at them.

When clearing a descriptor, the code has the usual select off by one
error when setting sync_io_nfds.

I don't see how this code could ever have worked correctly.

I have appended a patch for the problems I found.