BUILD: mworker: fix ignoring return value of ‘read’

Fix read return value unused result.

src/haproxy.c: In function ‘main’:
src/haproxy.c:3630:17: error: ignoring return value of ‘read’ declared with attribute ‘warn_unused_result’ [-Werror=unused-result]
 3630 |                 read(sock_pair[1], &c, 1);
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~

Must be backported where d7f6819 is backported.

Author: wlallemand

src/haproxy.c

@@ -3591,6 +3591,7 @@ int main(int argc, char **argv)
 		int sock_pair[2];
 		char *msg = NULL;
 		char c;
+		int r __maybe_unused;
 
 		if (socketpair(PF_UNIX, SOCK_STREAM, 0, sock_pair) == -1) {
 			ha_alert("[%s.main()] Cannot create socketpair to update the new worker state\n",
@@ -3626,8 +3627,8 @@ int main(int argc, char **argv)
 		 * after confirming receipt of the "\n" from the CLI applet, so
 		 * we make sure that the fd is received correctly.
 		 */
-                shutdown(sock_pair[1], SHUT_WR);
-		read(sock_pair[1], &c, 1);
+		shutdown(sock_pair[1], SHUT_WR);
+		r = read(sock_pair[1], &c, 1);
 		close(sock_pair[1]);
 		close(sock_pair[0]);
 		ha_free(&msg);