Darwin system and stdenv.hostPlatform features

Development
1

I am trying to fix Stockfish build on Darwin, which has been broken for years.

I’ve managed to do it, I needed to set CXX (because the Makefile uses g++):

makeFlags = [ "PREFIX=$(out)" "ARCH=${arch}" "CXX=${stdenv.cc.targetPrefix}c++" ];

And I needed to disable LTO, which is broken on Darwin, so I needed to remove a few lines from the Makefile, but sed can do it easily:

preBuild = stdenv.lib.optionalString stdenv.isDarwin ''
  sed -i.orig '/^\#\#\# 3.*Link Time Optimization/,/^\#\#\# 3/d' Makefile
'';

And it builds now without issues.

My problem is I need to set the proper value for ARCH, this is, if the CPU supports SSE4.2, ARCH should be "x86-64-modern" instead of "x86-64" (I am copying this from Homebrew’s formula). So, I tried to do this:

  arch64 = if stdenv.hostPlatform.sse4_2Support then "x86-64-modern" else "x86-64";
  arch = if stdenv.isx86_64 then arch64
         else if stdenv.isi686 then "x86-32"
         else "unknown";

But, even when building the derivation on a Macbook Pro which does supports SSE4.2,
all the SSE features of stdenv.hostPlatform are set to false and arch is set to "x86-64".

Is there a way to make the system detect that it supports SSE4.2, or is it not supported on Darwin?

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