Some Arduino implementations are incompatible with C, consider renaming to Shell.cpp

[me21]

I get the following errors when building:

In file included from C:\users\fgka\.platformio\packages\framework-arduinoststm32-maple\STM32F1\cores\maple/wirish.h:58:0,
                 from C:\users\fgka\.platformio\packages\framework-arduinoststm32-maple\STM32F1\cores\maple/Arduino.h:30,
                 from .pio\libdeps\sam_v1\GeekFactory Shell Library_ID1946\Shell.h:31,
                 from .pio\libdeps\sam_v1\GeekFactory Shell Library_ID1946\Shell.c:20:
C:\users\fgka\.platformio\packages\framework-arduinoststm32-maple\STM32F1\cores\maple/ext_interrupts.h:90:6: error: conflicting types for 'attachInterrupt'
 void attachInterrupt(uint8 pin, voidArgumentFuncPtr handler, void *arg,
      ^~~~~~~~~~~~~~~
C:\users\fgka\.platformio\packages\framework-arduinoststm32-maple\STM32F1\cores\maple/ext_interrupts.h:69:6: note: previous declaration of 'attachInterrupt' was here
 void attachInterrupt(uint8 pin, voidFuncPtr handler, ExtIntTriggerMode mode);
      ^~~~~~~~~~~~~~~

Arduino Maple core for STM32 is incompatible with C.
If I rename Shell.c to Shell.cpp, the problem goes away. The compiler builds everything in CPP mode then.