libevent: disable openssl for host

As host-libevent does not depend on host-openssl, it might attempt to
build against the host installed openssl. This does not work very well
on various hosts. Since we don't really need encryption support in
host-libevent just disable openssl support.

Disable build of example code as we already do for the target libevent.

Should fix:
http://autobuild.buildroot.net/results/403/403886e3afc6d5d18a138f4b0651f3c5a50ed064/
http://autobuild.buildroot.net/results/a2a/a2a84692049b0fb8038f1ad4b06554ecdac32e3c/
http://autobuild.buildroot.net/results/a36/a36abb1ac556a8b50e140ea1851955744b152608/



Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>