CI failure on NetBSD

On NetBSD 10.0, there is now a compilation error:

In file included from ../../src/m4.c:23:
=2E./../src/m4.h:192:14: error: conflicting types for =E2=80=98shquote=E2=
=80=99
  192 | extern char *shquote (char const *);
      |              ^~~~~~~
In file included from ../lib/stdlib.h:39,
                 from ../lib/unistd.h:124,
                 from ../lib/string.h:72,
                 from ../../src/m4.h:36,
                 from ../../src/m4.c:23:
/usr/include/stdlib.h:351:8: note: previous declaration of =E2=80=98shquote=
=E2=80=99 was here
  351 | size_t shquote(const char *, char *, size_t);
      |        ^~~~~~~
=2E./../src/m4.c:186:1: error: conflicting types for =E2=80=98shquote=E2=80=
=99
  186 | shquote (char const *arg)
      | ^~~~~~~
In file included from ../lib/stdlib.h:39,
                 from ../lib/unistd.h:124,
                 from ../lib/string.h:72,
                 from ../../src/m4.h:36,
                 from ../../src/m4.c:23:
/usr/include/stdlib.h:351:8: note: previous declaration of =E2=80=98shquote=
=E2=80=99 was here
  351 | size_t shquote(const char *, char *, size_t);
      |        ^~~~~~~
*** Error code 1

Stop.
make[2]: stopped in /home/runner/work/ci-check/ci-check/m4-2026-07-13/build=
/src


The function shquote was introduced in src/m4.h in
commit 3f8603dbd1562f2f3e7403716e0b81c7f0ba20b9 (2026-07-01).

It is a libc function on NetBSD, see <https://man.netbsd.org/shquote.3>.

Bruno