minor changes in CMakelists.txt for building on RHEL7.6. Note, the optional packages in

/etc/yum.repos.d/redhat.repo by setting "enabled = 1" in [rhel-6-server-optional-rpms] section

cmake_targets/tools/build_helper

@@ -102,6 +102,7 @@ check_supported_distribution() {
         "ubuntu14.04") return 0 ;;
         "fedora24")    return 0 ;;
         "rhel7")       return 0 ;;
+	"rhel7.6")     return 0 ;; 
         "centos7")     return 0 ;;
     esac
     return 1