Reset signal mask after fork

wlroots uses wl_event_loop_add_signal to handle SIGUSR1 from Xwayland.
wl_event_loop_add_signal works by masking the signal and receiving it from a
signalfd. The signal mask is preserved across fork and exec, so subprocesses
spawned by Sway start with SIGUSR1 masked. Most subprocesses do not expect this
and never unmask the signal, resulting in missing functionality or unexpected
behavior for processes that use SIGUSR1 (such as i3status).

Fix this by unmasking all signals between fork and exec.

sway/commands/exec_always.c

@@ -4,6 +4,7 @@
 #include <string.h>
 #include <sys/wait.h>
 #include <unistd.h>
+#include <signal.h>
 #include "sway/commands.h"
 #include "sway/config.h"
 #include "sway/tree/container.h"
@@ -47,6 +48,9 @@ struct cmd_results *cmd_exec_always(int argc, char **argv) {
 	if ((pid = fork()) == 0) {
 		// Fork child process again
 		setsid();
+		sigset_t set;
+		sigemptyset(&set);
+		sigprocmask(SIG_SETMASK, &set, NULL);
 		close(fd[0]);
 		if ((child = fork()) == 0) {
 			close(fd[1]);

sway/config/bar.c

@@ -10,6 +10,7 @@
 #include <sys/stat.h>
 #include <signal.h>
 #include <strings.h>
+#include <signal.h>
 #include "sway/config.h"
 #include "stringop.h"
 #include "list.h"
@@ -175,6 +176,9 @@ void invoke_swaybar(struct bar_config *bar) {
 	if (bar->pid == 0) {
 		setpgid(0, 0);
 		close(filedes[0]);
+		sigset_t set;
+		sigemptyset(&set);
+		sigprocmask(SIG_SETMASK, &set, NULL);
 
 		// run custom swaybar
 		size_t len = snprintf(NULL, 0, "%s -b %s",