pico/status_led.h might need extern "C"

[jdfin]

If I include pico/status_led.h from a cpp file, I end up with undefined symbols at link time. If I wrap the include in extern "C", it works.

The undefined symbols are cyw43_gpio_set and similar; I can see that there are no extern Cs by the time the includes get to cyw43_gpio_set in cyw43.h. I can bring up status_blink.cpp.obj file in an editor and it looks like it wants a mangled name (_Z14cyw43_gpio_setP8_cyw43_ti) but I'm guessing there.

To reproduce:
This is for pico2-w.
Create a new project from example status_blink.
Build it and copy the uf2 to the pico2-w and it works.
Rename status_blink.c to status_blink.cpp and change CMakeLists.txt accordingly.
Clean (delete build dir) and rebuild, and the link fails.
Wrap the #include "pico/status_led.h" in extern "C" and the build works, and the uf2 works.

The link error:

[build] C:/Users/johnf/.pico-sdk/toolchain/14_2_Rel1/bin/../lib/gcc/arm-none-eabi/14.2.1/../../../../arm-none-eabi/bin/ld.exe: CMakeFiles/status_blink.dir/status_blink.cpp.obj: in function `status_led_get_state':
[build] C:/Users/johnf/.pico-sdk/sdk/2.2.0/src/rp2_common/pico_status_led/include/pico/status_led.h:234:(.text.status_led_get_state+0x10): undefined reference to `cyw43_gpio_get(_cyw43_t*, int, bool*)'

I don't know where the extern "C" should go, or if it might cause other problems by putting it around the include of cyw43.h in status_led.h.

[kilograham]

@lurch seems like a good new python script to check ;-)