compositor/shared: Suppress write(2) warnings

Fixes the following warnings when building with _FORTIFY_SOURCE
and optimizations enabled:

../shared/xalloc.h:49:9: error: ignoring return value of ‘write’ declared with attribute ‘warn_unused_result’ [-Werror=unused-result]
   49 |         write(STDERR_FILENO, oommsg, strlen(oommsg));
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

or
../compositor/main.c:427:25: error: ignoring return value of ‘write’ declared with attribute ‘warn_unused_result’ [-Werror=unused-result]
  427 |                         write(STDERR_FILENO, fail_seteuid,
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  428 |                               strlen(fail_seteuid));
      |                               ~~~~~~~~~~~~~~~~~~~~~
../compositor/main.c:434:25: error: ignoring return value of ‘write’ declared with attribute ‘warn_unused_result’ [-Werror=unused-result]
  434 |                         write(STDERR_FILENO, fail_cloexec,
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  435 |                               strlen(fail_cloexec));
      |                               ~~~~~~~~~~~~~~~~~~~~~
../compositor/main.c:442:25: error: ignoring return value of ‘write’ declared with attribute ‘warn_unused_result’ [-Werror=unused-result]
  442 |                         write(STDERR_FILENO, fail_exec, strlen(fail_exec));
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
(cherry picked from commit 8c4cdd782e17aa587bfccb6746998571ddc90dd7)

compositor/main.c

@@ -385,6 +385,7 @@ weston_client_launch(struct weston_compositor *compositor,
 	sigset_t allsigs;
 	pid_t pid;
 	bool ret;
+	size_t written __attribute__((unused));
 
 	weston_log("launching '%s'\n", path);
 	str_printf(&fail_exec, "Error: Couldn't launch client '%s'\n", path);
@@ -424,22 +425,23 @@ weston_client_launch(struct weston_compositor *compositor,
 
 		/* Launch clients as the user. Do not launch clients with wrong euid. */
 		if (seteuid(getuid()) == -1) {
-			write(STDERR_FILENO, fail_seteuid,
-			      strlen(fail_seteuid));
+			written = write(STDERR_FILENO, fail_seteuid,
+					strlen(fail_seteuid));
 			_exit(EXIT_FAILURE);
 		}
 
 		ret = fdstr_clear_cloexec_fd1(&wayland_socket);
 		if (!ret) {
-			write(STDERR_FILENO, fail_cloexec,
-			      strlen(fail_cloexec));
+			written = write(STDERR_FILENO, fail_cloexec,
+					strlen(fail_cloexec));
 			_exit(EXIT_FAILURE);
 		}
 
 		execve(argp[0], argp, envp);
 
 		if (fail_exec)
-			write(STDERR_FILENO, fail_exec, strlen(fail_exec));
+			written = write(STDERR_FILENO, fail_exec,
+					strlen(fail_exec));
 		_exit(EXIT_FAILURE);
 
 	default:

compositor/xwayland.c

@@ -110,6 +110,7 @@ spawn_xserver(void *user_data, const char *display, int abstract_fd, int unix_fd
 	char *const *envp;
 	char *const *argp;
 	bool ret;
+	size_t written __attribute__ ((unused));
 
 	if (os_socketpair_cloexec(AF_UNIX, SOCK_STREAM, 0, wayland_socket.fds) < 0) {
 		weston_log("wl connection socketpair failed\n");
@@ -174,8 +175,8 @@ spawn_xserver(void *user_data, const char *display, int abstract_fd, int unix_fd
 		/* execve does not return on success, so it failed */
 
 		if (exec_failure_msg) {
-			write(STDERR_FILENO, exec_failure_msg,
-			      strlen(exec_failure_msg));
+			written = write(STDERR_FILENO, exec_failure_msg,
+					strlen(exec_failure_msg));
 		}
 
 		_exit(EXIT_FAILURE);

shared/xalloc.h

@@ -40,13 +40,14 @@ static inline void *
 abort_oom_if_null(void *p)
 {
 	static const char oommsg[] = ": out of memory\n";
+	size_t written __attribute__((unused));
 
 	if (p)
 		return p;
 
-	write(STDERR_FILENO, program_invocation_short_name,
-	      strlen(program_invocation_short_name));
-	write(STDERR_FILENO, oommsg, strlen(oommsg));
+	written = write(STDERR_FILENO, program_invocation_short_name,
+		        strlen(program_invocation_short_name));
+	written = write(STDERR_FILENO, oommsg, strlen(oommsg));
 
 	abort();
 }