`foo` builds with `gcc-arm-embedded` but `bar` does not, with `pkgsCross.arm-embedded`.

hardfloat.nix

let
  nixos1809 = import (fetchTarball channel:nixos-18.09) {};

  file = nixos1809.writeTextFile {
    name = "file.c";
    text = ''
      #include <math.h>
      int _exit(int i){};
      int main()
      {
        float v = log(0.f);
        return 0;
      }
     '';
     };

  cmd = ''arm-none-eabi-gcc -mfloat-abi=hard ${file} -o file -lm -o $out'';


overlay = self : super : {
  /*

  # I Tried to override newlibCross with hardware floating point, but without success

  newlibCross = super.newlibCross.overrideAttrs (old : {
    configureFlags = old.configureFlags ++ ["--enable-newlib-hw-fp"];
  });
  */
};

in
{
# That one will work
foo = with nixos1809;
  runCommand "foo" {
    allowSubstitutes = false;
    buildInputs = [gcc-arm-embedded];
  }
  cmd;

# That one fails with
# error: /build/ccgJg8Xr.o uses VFP register arguments...
bar = with import (fetchTarball channel:nixpkgs-unstable) {overlays = [overlay];};
  runCommand "bar" {
    buildInputs = [pkgsCross.arm-embedded.buildPackages.gcc];
  }
  cmd;
}