new compilation error

Hi Patrice,

The CI reports a new compilation error:

/bin/bash ../libtool  --tag=CC   --mode=link x86_64-linux-gnu-gcc -D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fwrapv -fno-strict-aliasing -pipe -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64  -Wl,-E  -fstack-protector-strong -L/usr/local/lib  -o ctexi2any ctexi2any-texi2any.o libtexinfo-main.la libtexinfoxs.la libtexinfo-convert.la libtexinfo.la -L/usr/lib/x86_64-linux-gnu/perl/5.38/CORE -lperl            
libtool: link: x86_64-linux-gnu-gcc -D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fwrapv -fno-strict-aliasing -pipe -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -Wl,-E -fstack-protector-strong -o .libs/ctexi2any ctexi2any-texi2any.o  -L/usr/local/lib ./.libs/libtexinfo-main.so ./.libs/libtexinfoxs.so ./.libs/libtexinfo-convert.so ./.libs/libtexinfo.so -L/usr/lib/x86_64-linux-gnu/perl/5.38/CORE -lperl -Wl,-rpath -Wl,/usr/local/lib/texi2any/lib
/usr/bin/ld: ./.libs/libtexinfo-convert.so: undefined reference to `u32_to_u8'
collect2: error: ld returned 1 exit status
make[5]: *** [Makefile:3804: ctexi2any] Error 1
make[5]: Leaving directory '/home/runner/work/ci-check/ci-check/texinfo/tta/C'
make[4]: *** [Makefile:3202: all] Error 2

The use of u32_to_u8 was introduced in commit 88e81219ee3fb010464f82d93c1812dd97e017a3,
three days ago.
(By the way, for converting a single UTF-32 character to UTF-8, the function
u8_uctomb is easier to use.
https://www.gnu.org/software/libunistring/manual/html_node/Creating-Unicode-strings.html )

I guess that the gnulib-tool invocation needs to consider module 'unistr/u32-to-u8'.

Bruno