Read and apply custom build option on flash page

[mituritsyn]

Is your feature request related to a problem? Please describe

not related to problem

Describe the solution you'd like

At current BFC will read and apply build options used in the firmware but will ignore custom defines

Describe alternatives you've considered

parse and apply custom defines too
for example, having following config after reflash I'll lost custom define for POS_HOLD_OPTION

https://build.betaflight.com/api/builds/f47415a1ce059c7d9b65b7d620e02351/log

Other information

No response

[haslinghuis]

Already planned to add altitude hold and position hold to firmware build options in betaflight/betaflight#13974 but position hold is still in progress. There are a lot of custom defines possible.

[mituritsyn]

Already planned to add altitude hold and position hold to firmware build options in betaflight/betaflight#13974 but position hold is still in progress. There are a lot of custom defines possible.

poshold was just an example there always will be a bunch of other custom options

[nerdCopter]

agree, would be nice if "auto-detect" populated the "custom defines".