* * Updated the build system for Mac
* Catalina env. uses Python 3.8 in MacPorts, Homebrew, and Anaconda3.
* Use Ruby 2.7 in MacPorts.
* Test build for macOS "Big Sur" (11.0) on Intel Mac "Catalina" (10.15.7).
* Updated the build system for macOS, including the future support for Big Sur (11.0)