general: fix compiler warning about unused results

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/dbus.c

@@ -1435,7 +1435,10 @@ static bool cdbus_process_windows_root_introspect(session_t *ps, DBusMessage *ms
 			continue;
 		}
 		char *tmp = NULL;
-		asprintf(&tmp, "<node name='%#010x'/>\n", w->id);
+		if (asprintf(&tmp, "<node name='%#010x'/>\n", w->id) < 0) {
+			log_fatal("Failed to allocate memory.");
+			abort();
+		}
 		mstrextend(&ret, tmp);
 		free(tmp);
 	}

src/log.c

@@ -256,7 +256,7 @@ static void file_logger_write(struct log_target *tgt, const char *str, size_t le
 static void file_logger_writev(struct log_target *tgt, const struct iovec *vec, int vcnt) {
 	auto f = (struct file_logger *)tgt;
 	fflush(f->f);
-	writev(fileno(f->f), vec, vcnt);
+	ssize_t _ attr_unused = writev(fileno(f->f), vec, vcnt);
 }
 
 static void file_logger_destroy(struct log_target *tgt) {

src/picom.c

@@ -2560,7 +2560,11 @@ int main(int argc, char **argv) {
 			// Notify the parent that we are done. This might cause the parent
 			// to quit, so only do this after setsid()
 			int tmp = 1;
-			write(pfds[1], &tmp, sizeof tmp);
+			if (write(pfds[1], &tmp, sizeof tmp) != sizeof tmp) {
+				log_fatal("Failed to notify parent process");
+				ret_code = 1;
+				break;
+			}
 			close(pfds[1]);
 			// We only do this once
 			need_fork = false;

src/utils.c

@@ -27,7 +27,7 @@ void report_allocation_failure(const char *func, const char *file, unsigned int
 	    {.iov_base = (void *)msg2, .iov_len = sizeof(msg2) - 1},
 	};
 
-	writev(STDERR_FILENO, v, ARR_SIZE(v));
+	ssize_t _ attr_unused = writev(STDERR_FILENO, v, ARR_SIZE(v));
 	abort();
 
 	unreachable;