brew install pothosware/pothos/airspyhf fails on M2 macs (depends on /usr/local)

[dl1ycf]

There seems to be a hard-coded assumption that include files are in /usr/local:

==> Reinstalling pothosware/pothos/soapyairspyhf
==> Installing dependencies for pothosware/pothos/soapyairspyhf: pothosware/pothos/airspyhf
==> Installing pothosware/pothos/soapyairspyhf dependency: pothosware/pothos/airspyhf
==> cmake .. -DLIBUSB_INCLUDE_DIR=/usr/local/include/libusb-1.0
==> make install
Last 15 lines from /Users/chwu/Library/Logs/Homebrew/airspyhf/02.make:
34 | #include <libusb.h>
| ^~~~~~~~~~
/tmp/airspyhf-20250304-47013-nbje2a/airspyhf-1.0/libairspyhf/src/airspyhf.c:34:10: fatal error: 'libusb.h' file not found
34 | #include <libusb.h>
| ^~~~~~~~~~
1 error generated.

but on M2 macs, the LIBUSB_INCLUDE_DIR is /opt/homebrew/include/libusb-1.0,
if $CPATH exists one should uses $CPATH/libusb-1.0