When resizing a terminal window while tog is loading commits the
following error will trigger occasionally:

	tog: poll: Interrupted system call	

One way of triggering this deliberately is to start tog and resize
the terminal via keyboard shortcuts immediately. This isn't 100%
reproducible, but I can usually trigger it after a few attempts.

The patch below ignores SIGWINCH while polling for a message from a
privsep helper. I've been unable to trigger the error with this so far.

There can now be a slight delay before tog's window gets updated after a
resize event. I think this is acceptable given that the current behaviour
results in a program exit.

This code path is also used by got(1) but I don't think that's an issue.

Is this a correct fix or is there a better solution?

-----------------------------------------------
commit 7dd602c8b5180d12decec8796190f9199f68079d (sigwinch)
from: Stefan Sperling <stsp@stsp.name>
date: Mon May 10 11:20:45 2021 UTC
 
 ignore SIGWINCH while polling in the main process
 
diff cffede58c8bec05ab17852de500cfc7225ef8fdc 3e1a4394edfb54bfb6c6119a22436d029c3c68ce
blob - df3a4a17cfe53a165183f57fb4a0eebe62acab91
blob + 97229123f0a5c6b797ce37122fe5960b948d80cc
--- lib/privsep.c
+++ lib/privsep.c
@@ -22,6 +22,7 @@
 
 #include <ctype.h>
 #include <limits.h>
+#include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -59,12 +60,22 @@ static const struct got_error *
 poll_fd(int fd, int events, int timeout)
 {
 	struct pollfd pfd[1];
+	struct timespec ts;
+	sigset_t sigset;
 	int n;
 
 	pfd[0].fd = fd;
 	pfd[0].events = events;
 
-	n = poll(pfd, 1, timeout);
+	ts.tv_sec = timeout;
+	ts.tv_nsec = 0;
+
+	if (sigemptyset(&sigset) == -1)
+		return got_error_from_errno("sigemptyset");
+	if (sigaddset(&sigset, SIGWINCH) == -1)
+		return got_error_from_errno("sigaddset");
+
+	n = ppoll(pfd, 1, timeout == INFTIM ? NULL : &ts, &sigset);
 	if (n == -1)
 		return got_error_from_errno("poll");
 	if (n == 0)