[Csnd-dev] building on RPi...

I'm having an issue building on a RPi Zero 2 w. Some warnings are being
treated as errors(see below), but I can't seem to disable this behaviour in
Cmake even though I have added the following to my Custom.cmake file:

set(CMAKE_COMPILE_WARNING_AS_ERROR OFF)

Anyone have any ideas?

/home/rory/sourcecode/csound/Engine/fgens.c: In function 'isstrcod':
/home/rory/sourcecode/csound/Engine/fgens.c:46:9: error: unused variable
'sel' [-Werror=unused-variable]
   46 |     int sel = (byte_order()+1)&1;
      |         ^~~
cc1: all warnings being treated as errors