mp4v2: fix build on darwin

pkgs/development/libraries/mp4v2/default.nix

@@ -19,6 +19,9 @@ stdenv.mkDerivation rec {
       url = "https://git.archlinux.org/svntogit/packages.git/plain/trunk/libmp4v2-c++11.patch?id=203f5a72bc97ffe089b424c47b07dd9eaea35713";
       sha256 = "0sbn0il7lmk77yrjyb4f0a3z3h8gsmdkscvz5n9hmrrrhrwf672w";
     })
+  ] ++ stdenv.lib.optionals stdenv.cc.isClang [
+    # unbreak build with Clang≥6 (C++14 by default). Based on https://reviews.freebsd.org/rP458678
+    ./fix-build-clang.patch
   ];
 
   NIX_CFLAGS_COMPILE = [ "-Wno-error=narrowing" ];

pkgs/development/libraries/mp4v2/fix-build-clang.patch

@@ -0,0 +1,13 @@
+diff --git a/src/mp4.cpp b/src/mp4.cpp
+index c2a7238..9bb3e38 100644
+--- a/src/mp4.cpp
++++ b/src/mp4.cpp
+@@ -870,7 +870,7 @@ MP4FileHandle MP4ReadProvider( const char* fileName, const MP4FileProvider* file
+         }
+ 
+         catch (...) {
+-            return MP4_INVALID_TRACK_ID;
++            return NULL;
+         }
+     }
+