doc: Mention an mknod bug

[Bruno Haible]

In m4/mknod.m4 there is a workaround against a bug found on macOS and
DragonFly. Let me document it.


2024-08-30  Bruno Haible  <bruno@clisp.org>

        doc: Mention an mknod bug.
        * doc/posix-functions/mknod.texi: Mention the S_IFIFO flag bug.

diff --git a/doc/posix-functions/mknod.texi b/doc/posix-functions/mknod.texi
index 3261abfdf3..923d951337 100644
--- a/doc/posix-functions/mknod.texi
+++ b/doc/posix-functions/mknod.texi
@@ -15,6 +15,11 @@
 This function mishandles trailing slash on some platforms:
 FreeBSD 7.2, Solaris 9.
 @item
+This function does not handle the @code{S_IFIFO} flag on some platforms:
+macOS 14, DragonFly 6.0,
+@c https://dev.haiku-os.org/ticket/19032
+Haiku.
+@item
 This function is missing on some platforms; however, the replacement
 always fails with @code{ENOSYS}: