tools: Use fputc() calls in some functions

[Markus Elfring]

…
> All errors (new ones prefixed by >>):
> 
>>> builtin-check.c:300:8: error: incompatible pointer to integer conversion passing 'FILE *' (aka 'struct _IO_FILE *') to parameter of type 'int' [-Wint-conversion]
>      300 |         fputc(stderr, '\n');
>          |               ^~~~~~
>    /usr/include/stdio.h:155:16: note: expanded from macro 'stderr'
>      155 | #define stderr stderr
>          |                ^~~~~~
>    /usr/include/stdio.h:611:23: note: passing argument to parameter '__c' here
>      611 | extern int fputc (int __c, FILE *__stream) __nonnull ((2));
>          |                       ^…

Would you become interested to take another look at a corrected source code transformation approach?

Improving output for single characters (with SmPL)?
https://lore.kernel.org/cocci/406093f5-ee7d-4ae9-808b-2b42d4846eab@web.de/
https://sympa.inria.fr/sympa/arc/cocci/2026-07/msg00055.html
https://lkml.org/lkml/2026/7/23/2205

Can similar adjustments become more helpful for further software areas?

Regards,
Markus