package/openvmtools: do not force -I/usr/include in CPPFLAGS

Fixes:
    http://autobuild.buildroot.net/results/447/4473d8a99ffec1fde491d172520e86ae1e69fae7/



[Thomas: change patch sequence number to 05, since another patch added
a 04 patch in the mean time.]

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