anchor.diff:      ++ optional withDoc "info"; # it's dev-doc only
     outputBin = "dev"; # fftw-wisdom
   
  +  buildInputs = lib.optionals stdenv.cc.isClang [
  +    # TODO: This may mismatch the LLVM version sin the stdenv, see #79818.
  +    llvmPackages.openmp
  +  ];
  +
     configureFlags =
       [ "--enable-shared"
         "--enable-threads"
  
positive.code: { fetchurl, stdenv, lib, precision ? "double", perl }:
  
  with lib;
  
  assert elem precision [ "single" "double" "long-double" "quad-precision" ];
  
  let
  
negative.code:     # all x86_64 have sse2
      # however, not all float sizes fit
      ++ optional (stdenv.isx86_64 && (precision == "single" || precision == "double") )  "--enable-sse2"
      ++ [ "--enable-openmp" ]
      # doc generation causes Fortran wrapper generation which hard-codes gcc
      ++ optional (!withDoc) "--disable-doc";
  
  