error building gcl-2.7.1 on x86_64-pc-linux-gnu with GCC 16.1.0

Ciao,

  I  am a  casual,  beginner user;  on a  Slackware64  15.0, running  on
x86_64-pc-linux-gnu, I have installed GCC 16.1.0 from a release tarball;
trying to compile GCL 2.7.1 I see:

cd gcl-2.7.1
./configure --prefix=/opt/gcl/2.7.1/
make
...
/opt/gcc/16.1.0/bin/gcc -DHAVE_CONFIG_H -I. -I./h  -I h -I /usr/include/tirpc   -fsigned-char -pipe -fcommon -fno-builtin-malloc -fno-builtin-free -fno-PIE -fno-pie -fno-PIC -fno-pic -std=gnu17 -Wall -Wno-empty-body -Wno-unused-but-set-variable -D_FILE_OFFSET_BITS=64 -D_TIME_BITS=64  -I/usr/include/tirpc   -O3 -fomit-frame-pointer -I o  -MT o/main.o -MD -MP -MF $depbase.Tpo -c -o o/main.o o/main.c &&\
mv -f $depbase.Tpo $depbase.Po
o/main.c:1436:32: warning: 'enum disassembler_style' declared inside parameter list will not be visible outside of this definition or declaration
 1436 | my_fprintf_styled(void *v,enum disassembler_style,const char *f,...) {
      |                                ^~~~~~~~~~~~~~~~~~
o/main.c:1436:27: error: parameter 2 has incomplete type
 1436 | my_fprintf_styled(void *v,enum disassembler_style,const char *f,...) {
      |                           ^~~~~~~~~~~~~~~~~~~~~~~
In file included from ./h/../h/compbas.h:1,
                 from ./h/include.h:108,
                 from o/main.c:46:
o/main.c: In function 'my_fprintf_styled':
o/main.c:1439:3: error: 'va_start' used in function with fixed arguments
 1439 |   va_start(va,f);
      |   ^~~~~~~~
make[1]: *** [Makefile:1825: o/main.o] Error 1
make[1]: Leaving directory '/home/marco/var/build/devel/gcl-2.7.1'
make: *** [Makefile:1044: all] Error 2

I  cannot be  the  only one  seeing  this, but  I  cannot find  anything
searching the archive or in the bugs page.

  Do I have to use an old GCC?

Thanks.
-- 
Marco Maggi