pico_btstack_make_gatt_header broken when specifying files without path

[Slion]

While working on pico-demo-gatt-service I realized that pico_btstack_make_gatt_header is broken unless you specify a path for your GATT file. File names without path break the build with the following error:

Keyword WORKING_DIRECTORY requires a value, but none was given.

To reproduce the issue you can use the example linked above and remove the path ${CMAKE_CURRENT_LIST_DIR}/ from the GATT file name.

[will-v-pi]

There are plenty of other SDK functions that also require you to specify the full path (ie prefixed with ${CMAKE_CURRENT_LIST_DIR}), eg pico_generate_pio_header, pico_sign_binary, pico_embed_pt_in_binary - this is because you can't guarantee the current working directory CMake is in for custom commands, so need a full path to any files being used in those functions that use custom commands.

[Slion]

If that's really needed then maybe an explicit error message could help. Feel free to close the ticket though. At least that error message is recorded here and it should help others and myself next time around.

[kilograham]

I think it is reasonable to check in this case, since the error message is confusing, and we're explicitly splitting out the path in our code and expecting it to be present (this is subtly different from just the filename not being found)

[kilograham]

merged into develop