Support macOS versions older than Sierra

[krksgbr]

Running the backend on macOS versions older than Sierra will crash with:

Dyld Error Message:
  Symbol not found: _clock_gettime
  Referenced from: /Applications/GlyphCollector.app/Contents/Resources/app/dist/glyphcollector (which was built for Mac OS X 10.12)
  Expected in: /Applications/GlyphCollector.app/Contents/Resources/app/dist/libSystem.B.dylib

Related information:

• https://gitlab.haskell.org/ghc/ghc/wikis/building/preparation/mac-osx#supporting-older-os-x-versions-with-your-build

• https://gitlab.haskell.org/ghc/ghc/issues/12858

• https://gitlab.haskell.org/ghc/ghc/issues/17895

• https://gitlab.haskell.org/ghc/ghc/issues/17895