Fix "host networked game" option

It was broken by b95c9996bf because
ignoring SIGCHLD makes it impossible to query exit status of wesnothd
subprocess. Fix this by spawning a thread to wait for the browser
instead of ignoring SIGCHLD.

src/desktop/open.cpp

@@ -19,6 +19,8 @@
 
 #if defined(_X11) || defined(__APPLE__)
 
+#include <thread>
+
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <unistd.h> // fork(), exec family
@@ -74,8 +76,8 @@ bool open_object(const std::string& path_or_url)
 		_exit(1); // This shouldn't happen.
 	}
 
-	// Waiting for the child process to exit is unnecessary because we ignore SIGCHLD.
-	// See the manpage for wait(2).
+	std::thread t { [child](){ int status; waitpid(child, &status, 0); } };
+	t.detach();
 
 	return true;
 

src/wesnoth.cpp

@@ -1099,11 +1099,6 @@ int main(int argc, char** argv)
 	sigemptyset(&terminate_handler.sa_mask);
 	sigaction(SIGTERM, &terminate_handler, nullptr);
 	sigaction(SIGINT, &terminate_handler, nullptr);
-
-	// Explicitly ignore SIGCHLD. This allows us to launch child processes without waiting
-	// for them to exit. See the manpage for wait(2).
-	terminate_handler.sa_handler = SIG_IGN;
-	sigaction(SIGCHLD, &terminate_handler, nullptr);
 #endif
 
 	// declare this here so that it will always be at the front of the event queue.