armclang: specify armlink link executable signature

The default armlink signature uses `--list=<TARGET_BASE>.map`, but in
Zephyr we uses a different name for the map file, therefore we need to
specify a custom link executable signature.

This is done in the linker specific flags file:
cmake/linker/armlink/linker_flags.cmake

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>