make RadioLib build compatible with Arduino Core for CH32

[lyusupov]

Arduino Core for CH32 EVT Boards ( https://github.com/openwch/arduino_core_ch32 ) is very similar to other Arduino Cores except that it uses a different attachInterrupt() semantic:
https://github.com/openwch/arduino_core_ch32/blob/main/cores/arduino/WInterrupts.h#L27

Author of the CH32 Core has some objections against use of a standard attachInterrupt()
see this ticket for details: openwch/arduino_core_ch32#15

This PR is intended to apply a workaround to the RadioLib (if possible) to allow a build of the library together with Arduino CH32 Core.

I've tested the patch with a sketch for CH32V307 that now builds successfully with RadioLib 7.1.0 and 'master' branch of Arduino Core for CH32.

[jgromes]

I don't think this is a good approach. Arduino has defined API, that includes having signatures for different functions, including attachInterrupt. Dozens of Arduino cores use it, why can't the CH32? I've added a comment to that effect in the issue linked above.