They're useless, and I have no idea what they're actually supposed to do
(wrt. pending input processing changes).
Also remove their implicit uses from the IPC handlers.
This workaround prevented that libmpv users could accidentally crash
when the SIGPIPE signal was triggered by FFmpeg's OpenSSL/GnuTLS usage.
But it also modifies the global signal handler state, so remove it now
that this workaround is not required anymore.
For clang, it's enough to just put (void) around usages we are
intentionally ignoring the result of.
Since GCC does not seem to want to respect this decision, we are forced
to disable the warning globally.
This implements the JSON IPC protocol with named pipes, which are
probably the closest Windows equivalent to Unix domain sockets in terms
of functionality. Like with Unix sockets, this will allow mpv to listen
for IPC connections and handle multiple IPC clients at once. A few cross
platform libraries and frameworks (Qt, node.js) use named pipes for IPC
on Windows and Unix sockets on Linux and Unix, so hopefully this will
ease the creation of portable JSON IPC clients.
Unlike the Unix implementation, this doesn't share code with
--input-file, meaning --input-file on Windows won't understand JSON
commands (yet.) Sharing code and removing the separate implementation in
pipe-win32.c is definitely a possible future improvement.
