* Remove F_SETSIG call from Linux on X11 display.
Presumably, this was added to be like the `I_SETSIG` call on Solaris.
But it is the only `F_SETSIG` done on Linux and there isn't an
equivalent on the other platforms that we support as it is a GNU
extension.
Also, `F_SETSIG` with an argument of `0`, as here, means to send
the `SIGIO` signal, which is what is done by default.
From the man page:
F_SETSIG (int)
Set the signal sent when input or output becomes possible
to the value given in arg. A value of zero means to send
the default SIGIO signal. Any other value (including SIGIO)
is the signal to send instead, and in this case additional
info is available to the signal handler if installed with
SA_SIGINFO.
By using F_SETSIG with a nonzero value, and setting
SA_SIGINFO for the signal handler (see sigaction(2)),
extra information about I/O events is passed to the
handler in a siginfo_t structure. If the si_code field
indicates the source is SI_SIGIO, the si_fd field gives
the file descriptor associated with the event. Otherwise,
there is no indication which file descriptors are
pending, and you should use the usual mechanisms
(select(2), poll(2), read(2) with O_NONBLOCK set etc.)
to determine which file descriptors are available for I/O.
We aren't setting a non-zero value and we aren't establishing signal
handlers via `sigaction` with `SA_SIGINFO` set, so this shouldn't
be doing anything important for us.
* Stop setting _GNU_SOURCE for GNU libc extensions.
We were previously doing this to get access to the
`F_SETSIG` flag for `fcntl`, but this isn't being
used any longer.
FILES USED IN THIS DIRECTORY
config.guess
config.sub taken from GNU project's "config" directory, on
prep.ai.mit.edu/pub/gnu/config. Update 'em as
needed.
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