libc/stdio/vsnprintf.c: add explicit fallthrough
silences recent GCC warning
@@ -164,6 +164,7 @@ print_format(char **buffer, size_t bufsize, const char *format, void *var)
break;
case 'X':
upper = true;
+ /* fallthrough */
case 'x':
sizec[i] = '\0';
value = (unsigned long) var & convert[length_mod];
