test/overlay builds every time

[Simon Glass]

Hi Maxime & Pantelis,

I notice that this directory always builds its files even if seemingly
nothing has changed:

  LD      test/built-in.o
  DTC     test/overlay/test-fdt-base.dtb
  DTB     test/overlay/test-fdt-base.dtb.S
  AS      test/overlay/test-fdt-base.dtb.o
  DTC     test/overlay/test-fdt-overlay.dtb
  DTB     test/overlay/test-fdt-overlay.dtb.S
  AS      test/overlay/test-fdt-overlay.dtb.o
  DTC     test/overlay/test-fdt-overlay-stacked.dtb
  DTB     test/overlay/test-fdt-overlay-stacked.dtb.S
  AS      test/overlay/test-fdt-overlay-stacked.dtb.o
  LD      test/overlay/built-in.o
  LD      u-boot

Do either of you know what might be causing this? Can we fix it?

Thanks,
Simon