build: use --gc-sections, -fvisibility=hidden

build: use --gc-sections, -fvisibility=hidden

After:
  # ls -l /sbin/udevadm /sbin/udevd /lib/udev/*_id
  -rwxr-xr-x 1 root root  22984 May 18 18:19 /lib/udev/ata_id
  -rwxr-xr-x 1 root root  31208 May 18 18:19 /lib/udev/cdrom_id
  -rwxr-xr-x 1 root root  27128 May 18 18:19 /lib/udev/input_id
  -rwxr-xr-x 1 root root  31272 May 18 18:19 /lib/udev/path_id
  -rwxr-xr-x 1 root root  31896 May 18 18:19 /lib/udev/scsi_id
  -rwxr-xr-x 1 root root  35456 May 18 18:19 /lib/udev/usb_id
  -rwxr-xr-x 1 root root   6416 May 18 18:19 /lib/udev/v4l_id
  -rwxr-xr-x 1 root root 130320 May 18 18:19 /sbin/udevadm
  -rwxr-xr-x 1 root root 134648 May 18 18:19 /sbin/udevd

Before:
  # ls -l /sbin/udevadm /sbin/udevd /lib/udev/*_id
  -rwxr-xr-x 1 root root  27208 May 18 18:22 /lib/udev/ata_id
  -rwxr-xr-x 1 root root  35456 May 18 18:22 /lib/udev/cdrom_id
  -rwxr-xr-x 1 root root  39584 May 18 18:22 /lib/udev/input_id
  -rwxr-xr-x 1 root root  39600 May 18 18:22 /lib/udev/path_id
  -rwxr-xr-x 1 root root  36056 May 18 18:22 /lib/udev/scsi_id
  -rwxr-xr-x 1 root root  43712 May 18 18:22 /lib/udev/usb_id
  -rwxr-xr-x 1 root root   6504 May 18 18:22 /lib/udev/v4l_id
  -rwxr-xr-x 1 root root 142656 May 18 18:22 /sbin/udevadm
  -rwxr-xr-x 1 root root 142888 May 18 18:22 /sbin/udevd