gstreamer: needs dynamic libraries

Fixes:
http://autobuild.buildroot.net/results/49d/49dcec0bd2f3bb78c18675a9fa5c9c53cc183fd2/



g_cclosure_marshal_VOID__VOID is defined both in libgobject.a and
libgstreamer.a. It is probably possible to fix this, but gstreamer0.10
has been deprecated for a long time now and is anyway unlikely to be
used in static-only situations, so let's just require dynamic linking.

Propagate to the reverse dependencies. opencv3 already did depend on
dynamic libs.

[Peter: add autobuild reference]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>