add_custom_command uses wrong arguments

[kilograham]

e.g.

    add_custom_command(TARGET xip_ram_perms
        COMMAND ${CMAKE_COMMAND} -E copy ${XIP_RAM_PERMS_ELF} ${CMAKE_BINARY_DIR}/xip_ram_perms.elf
        DEPENDS xip_ram_perms
    )

Newest CMake now complains about this:

1. you must now specify POST_BUILD explicitly
2. DEPENDS was always incorrect I guess

[will-v-pi]

This is fixed in picotool in #207 - I think similar fixes are also needed in the SDK tools/CMakeLists.txt

[kilograham]

could you make a PR for SDK too

[will-v-pi]

SDK PR merged into develop too