cmake: do not duplicate -Wall gcc flag for debug builds
cmake: do not duplicate -Wall gcc flag for debug builds

jsilhan/hawkey,yavor-atanasov/hawkey,MichaelMraka/hawkey,jsilhan/hawkey,yavor-atanasov/hawkey,mizdebsk/hawkey,jsilhan/hawkey,mluscon/hawkey,mizdebsk/hawkey,cgwalters/hawkey,rpm-software-management/hawkey,megaumi/hawkey,MichaelMraka/hawkey,mizdebsk/hawkey,cgwalters/hawkey,ignatenkobrain/hawkey,yavor-atanasov/hawkey,ignatenkobrain/hawkey,ignatenkobrain/hawkey,mluscon/hawkey,Conan-Kudo/hawkey,rholy/hawkey,rholy/hawkey,Conan-Kudo/hawkey,MichaelMraka/hawkey,Conan-Kudo/hawkey,rpm-software-management/hawkey,yavor-atanasov/hawkey,ignatenkobrain/hawkey,rholy/hawkey,cgwalters/hawkey,jsilhan/hawkey,mluscon/hawkey,megaumi/hawkey,Conan-Kudo/hawkey,rpm-software-management/hawkey,cgwalters/hawkey,MichaelMraka/hawkey,mluscon/hawkey,rpm-software-management/hawkey,megaumi/hawkey,megaumi/hawkey,mizdebsk/hawkey,rholy/hawkey