message: Use the `-isystem` flag to suppress warnings from `brew` dependencies
  By marking a folder as a system folder, the compiler will suppress
  warnings from code included from there.
diff: @@ -19,7 +19,7 @@ jobs:
  xcode: "12.5.1"
  environment:
  - HOMEBREW_NO_AUTO_UPDATE: 1
  - - WARN_EXTRA: "-Wno-double-promotion"
  + - WARN_EXTRA: "-isystem /usr/local/include"
  steps:
  - checkout
  - run: git submodule update --init nas2d-core/
  