ushare: do not allow building in static lib situations

The ushare configure script is a custom shell script, and it is not
designed to understand that the library order is important when doing
static linking.

Fixes:

  http://autobuild.buildroot.org/results/32e/32ed2a521043f929cc290145c8a651e69042e104/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>