Fix compile error in FreeBSD build
In FreeBSD's errno.h ERESTART is not defined by default, only when the user requests the pseudo-errors returned inside the kernel to be enabled. As a result the block where drmCommandWriteRead is called returns compile error. Defined _WANT_KERNEL_ERRNO to fix it (see FreeBSD's /usr/include/errno.h)
Signed-off-by: Eleni Maria Stea elene.mst@gmail.com