dts.overlay is not being appended

[SebastianBoe]

In the boot/zephyr build scripts it is stated that dts.overlay will be appended to the CLI-specified overlay file. But it is not.

# Add a common dts overlay necessary to ensure mcuboot is linked into,
# and fits inside, the boot partition. (If the user specified a
# DTC_OVERLAY_FILE on the CMake command line, we need to append onto
# the list).
if(DTC_OVERLAY_FILE)
  set(DTC_OVERLAY_FILE
      "${DTC_OVERLAY_FILE} ${CMAKE_CURRENT_LIST_DIR}/dts.overlay")
else()
  set(DTC_OVERLAY_FILE ${CMAKE_CURRENT_LIST_DIR}/dts.overlay)
endif()

When specifying DTC_OVERLAY_FILE we get the result:

sebo@mach:~/ncs/mcuboot/boot/zephyr$ rm -rf b && cmake -H. -Bb -DDTC_OVERLAY_FILE=/home/sebo/ncs/zephyr/misc/empty_file.c 
rm -rf b && cmake -H. -Bb -DDTC_OVERLAY_FILE=/home/sebo/ncs/zephyr/misc/empty_file.c 
Zephyr version: 1.13.99
-- Found PythonInterp: /home/sebo/bin/python3.4 (found suitable version "3.5.2", minimum required is "3.4") 
-- Selected BOARD qemu_x86
Parsing Kconfig tree in /home/sebo/ncs/mcuboot/boot/zephyr/Kconfig
Loading /home/sebo/ncs/zephyr/boards/x86/qemu_x86/qemu_x86_defconfig as base
Merging prj.conf
Configuration written to '/home/sebo/ncs/mcuboot/boot/zephyr/b/zephyr/.config'

warning: FLASH_MAP (defined at subsys/storage/flash_map/Kconfig:12) has direct dependencies FLASH_HAS_DRIVER_ENABLED with value n, but is currently being y-selected by the following symbols:
 - MCUBOOT_DEVICE_SETTINGS (defined at /home/sebo/ncs/mcuboot/boot/zephyr/Kconfig:207), with value y, direct dependencies "y" (value: y)
-- DTC_OVERLAY_FILE_AS_LIST: /home/sebo/ncs/zephyr/misc/empty_file.c
/home/sebo/ncs/zephyr/misc/empty_file.c
-- Loading /home/sebo/ncs/zephyr/boards/x86/qemu_x86/qemu_x86.dts as base
-- Overlaying /home/sebo/ncs/zephyr/dts/common/common.dts
-- Overlaying /home/sebo/ncs/zephyr/misc/empty_file.c
-- Cache files will be written to: /home/sebo/.cache/zephyr

which shows that dts.overlay is not being appended.