Compile error implicit-function-declaration

Hello,

build with enabled -Werror=implicit-function-declaration ends with error[1]:

> sanei_init_debug.c: In function ‘sanei_debug_msg’:
> sanei_init_debug.c:103:17: error: implicit declaration of function ‘isfdtype’; did you mean ‘isctype’? [-Werror=implicit-function-declaration]
>   103 |       if ( 1 == isfdtype(fileno(stderr), S_IFSOCK) )
>       |                 ^~~~~~~~
>       |                 isctype
> cc1: some warnings being treated as errors
> make[2]: *** [Makefile:68: sanei_init_debug.o] Error 1

CU Jörg

[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1066571