automake: don't enable -Wl,--no-undefined on OpenBSD

automake: don't enable -Wl,--no-undefined on OpenBSD

OpenBSD does not have DT_NEEDED entries for libc by design,
over concerns how the symbols would be referenced after
changing the major version of the library.

So avoid -no-undefined checks on OpenBSD as they will fail.

v2: don't include the -no-undefined libtool option in the variable
    and change -Wl,--no-undefined references in Automake.inc as well.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=76856
Signed-off-by: Jonathan Gray <jsg@jsg.id.au>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>