icewm: enable on darwin (#413470)

pkgs/by-name/ic/icewm/package.nix

···
 {
   lib,
-  stdenv,
+  gccStdenv,
   fetchFromGitHub,
   cmake,
   expat,
···
   pkg-config,
 }:
 
-stdenv.mkDerivation (finalAttrs: {
+gccStdenv.mkDerivation (finalAttrs: {
   pname = "icewm";
   version = "3.7.5";
 
···
     "-DPREFIX=$out"
     "-DCFGDIR=/etc/icewm"
   ];
+
+  env.NIX_CFLAGS_COMPILE = lib.optionalString gccStdenv.hostPlatform.isDarwin "-D_DARWIN_C_SOURCE";
 
   # install legacy themes
   postInstall = ''
···
       $out/share/icewm/themes/
   '';
 
-  meta = with lib; {
+  meta = {
     homepage = "https://ice-wm.org/";
     description = "Simple, lightweight X window manager";
     longDescription = ''
···
       optional external background wallpaper manager with transparency support,
       a simple session manager and a system tray.
     '';
-    license = licenses.lgpl2Only;
+    license = lib.licenses.lgpl2Only;
     maintainers = [ ];
-    platforms = platforms.linux;
+    platforms = lib.platforms.unix;
   };
 })