Ruby

Avoid warnings on MINGW:

win32/win32.c: In function 'rtc_error_handler':
win32/win32.c:691:5: warning: function 'rtc_error_handler' might be a candidate for 'gnu_printf' format attribute [-Wsuggest-attribute=format]
691 | rb_str_vcatf(str, fmt, ap);
| ^~~~~~~~~~~~

and

win32/win32.c:683:1: warning: 'rtc_error_handler' defined but not used [-Wunused-function]
683 | rtc_error_handler(int e, const char *src, int line, const char *exe, const char *fmt, ...)
| ^~~~~~~~~~~~~~~~~