package/nmap: Fix static linking

Fixes
http://autobuild.buildroot.net/results/040/040129539257d88d9437d113752bc8634fd9b2b2/
http://autobuild.buildroot.net/results/73a/73a562a3a1f356c1a39b2fb57f0848c4b99fe8b1/
http://autobuild.buildroot.net/results/767/767b8eafe7a204327eaa182c065ca5cfff18096f/
http://autobuild.buildroot.net/results/0f7/0f7f3a56815dc6422a466fe9b4357ace98f78e11/



[Peter: add host-pkgconf to _DEPENDENCIES]
Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>