configure.ac: bump pthread-stubs requirement

configure.ac: bump pthread-stubs requirement

On platforms that require it, we bump the requirement to 0.4 or later.
Due to an issue with the project [design] any version earlier than it,
is bound to cause issues. For the specifics see the pthread-stubs README

Cc: Uli Schlachter <psychon@znc.in>
Cc: Jonathan Gray <jsg@jsg.id.au>
Cc: Jean-Sébastien Pédron <dumbbell@FreeBSD.org>
Cc: François Tigeot <ftigeot@wolfpond.org>
Cc: Tobias Nygren <tnn@NetBSD.org>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>