libmad: build on Darwin

pkgs/development/libraries/libmad/default.nix

@@ -8,7 +8,11 @@ stdenv.mkDerivation rec {
     sha256 = "bbfac3ed6bfbc2823d3775ebb931087371e142bb0e9bb1bee51a76a6e0078690";
   };
 
-  patches = [ ./001-mips_removal_h_constraint.patch ./pkgconfig.patch ];
+  patches = [ ./001-mips_removal_h_constraint.patch ./pkgconfig.patch ]
+  # optimize.diff is taken from https://projects.archlinux.org/svntogit/packages.git/tree/trunk/optimize.diff?h=packages/libmad
+  # It is included here in order to fix a build failure in Clang
+  # But it may be useful to fix other, currently unknown problems as well
+  ++ stdenv.lib.optional (stdenv.cc.cc.isClang or false) [ ./optimize.diff ];
 
   nativeBuildInputs = [ autoconf ];
 
@@ -22,6 +26,7 @@ stdenv.mkDerivation rec {
   meta = with stdenv.lib; {
     homepage    = http://sourceforge.net/projects/mad/;
     description = "A high-quality, fixed-point MPEG audio decoder supporting MPEG-1 and MPEG-2";
+    license     = licenses.gpl2;
     maintainers = with maintainers; [ lovek323 ];
     platforms   = platforms.unix;
   };