mbed_die doesn't have access to LED1 when building with mbed-tools

Description of defect

When compiling for my custom targets and NRF52840_DK I see:

 Building C object CMakeFiles/BLE_GattServer_CharacteristicUpdates.dir/mbed-os/platform/source/mbed_board.c.obj
../../../../mbed-os/platform/source/mbed_board.c: In function 'mbed_die':
../../../../mbed-os/platform/source/mbed_board.c:31:12: warning: unused variable 'led_err' [-Wunused-variable]
   31 |     gpio_t led_err;

and this is because led_err is only used if LED1 is defined

Target(s) affected by this defect ?

NRF52840_DK but likely more

Toolchain(s) (name and version) displaying this defect ?

arm-none-eabi-gcc (GNU Tools for Arm Embedded Processors 9-2019-q4-major) 9.2.1 20191025 (release) [ARM/arm-9-branch revision 277599]

What version of Mbed-os are you using (tag or sha) ?

5fe4daf

What version(s) of tools are you using. List all that apply (E.g. mbed-cli)

mbed-tools 7.15.0

How is this defect reproduced ?

just build anything with NRF52 or perhaps other targets.

[adbridge]

Closed/reopened to retrigger the github action for issue handling.

Can somebody please verify whether this is a problem with other targets? If it does happen with other targets, then mbed_die will never do the flashy flashy on crash for a lot of people. If that's true, then the issue severity should be bumped.