mount: notice daemon dying much quicker

Before this change we waited until until the timeout to check the
daemon was alive.

Now we check it every 100ms like we do the mount status.

This also fixes compiling on all platforms which was broken by the
previous change

9bfbf2a4a mount: fix macOS not noticing errors with --daemon

See: https://forum.rclone.org/t/rclone-mount-daemon-exits-successfully-even-when-mount-fails/43146

cmd/mountlib/check_other.go

@@ -3,10 +3,6 @@
 
 package mountlib
 
-import (
-	"time"
-)
-
 // CheckMountEmpty checks if mountpoint folder is empty.
 // On non-Linux unixes we list directory to ensure that.
 func CheckMountEmpty(mountpoint string) error {
@@ -19,9 +15,5 @@ func CheckMountReady(mountpoint string) error {
 	return nil
 }
 
-// WaitMountReady should wait until mountpoint is mounted by rclone.
-// The check is implemented only for Linux so we just sleep a little.
-func WaitMountReady(mountpoint string, timeout time.Duration) error {
-	time.Sleep(timeout)
-	return nil
-}
+// CanCheckMountReady is set if CheckMountReady is functional
+var CanCheckMountReady = false