MKL and libm compile notes: macOS

You can instead specify these in a Make.user file.
Also, a couple warnings:

  1. MKL is incompatible with ARPACK, a dependency of packages such as Distributions and LightGraphs.
  2. SpecialFunctions.jl can take advantage of openlibm, but not intellibm, for much better performance. Not as severe as the above, because SpecialFunctions will still work. It can however be many times slower.