openvmtools: disable -Werror

Disable the mandatory flag -Werror in configure.ac.
This also makes -Wno-deprecated-declarations flag unnecessary.

Fixes:
  http://autobuild.buildroot.net/results/440/4400abc17115d0f5eb65c4eb012f11766cbe5a56/
  http://autobuild.buildroot.net/results/02b/02b24a012dbc76e366c10d3758978eba5e597499/



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