Added check for pkg-config so that build only use related package checks when  it's supported
Added check for pkg-config so that build only use related package checks when 
it's supported


ntoand/osg,XiaoCC/osg,XiaoCC/osg,omega-hub/osg,koshman86/osg,ghub/osg,artoolkit/osg,stmh/osg,omega-hub/osg,omega-hub/osg,omega-hub/osg,koshman86/osg,stmh/osg,koshman86/osg,stmh/osg,stmh/osg,XiaoCC/osg,ghub/osg,ghub/osg,artoolkit/osg,XiaoCC/osg,koshman86/osg,XiaoCC/osg,artoolkit/osg,ntoand/osg,artoolkit/osg,ghub/osg,ntoand/osg,stmh/osg,ntoand/osg