Recognize "macOS" as a valid issue (autotools)

Author: d-torrance

M2/configure.ac

@@ -115,7 +115,7 @@ then if test -f /usr/bin/sw_vers
      fi
      # translate to something standard (for us), and verify :
      case $ISSUE_FLAVOR in
-         "Mac OS X") ISSUE_FLAVOR=MacOS ;;
+         "Mac OS X"|"macOS") ISSUE_FLAVOR=MacOS ;;
 	 "debian"|"Debian"*) ISSUE_FLAVOR=Debian ;;
          "ubuntu"|"Ubuntu") ISSUE_FLAVOR=Ubuntu ;;
 	 "FedoraCore"*) ISSUE_FLAVOR=FedoraCore ;;