libtheora: add mingw support

Part of a larger effort to add mingw support for qtmultimedia

pkgs/development/libraries/libtheora/default.nix

@@ -15,6 +15,8 @@ stdenv.mkDerivation rec {
       url = "https://github.com/xiph/theora/commit/28cc6dbd9b2a141df94f60993256a5fca368fa54.diff";
       sha256 = "16jqrq4h1b3krj609vbpzd5845cvkbh3mwmjrcdg35m490p19x9k";
     })
+  ] ++ lib.optionals stdenv.hostPlatform.isMinGW [
+    ./mingw-remove-export.patch
   ];
 
   configureFlags = [ "--disable-examples" ];
@@ -30,6 +32,6 @@ stdenv.mkDerivation rec {
     description = "Library for Theora, a free and open video compression format";
     license = licenses.bsd3;
     maintainers = with maintainers; [ ];
-    platforms = platforms.unix;
+    platforms = platforms.unix ++ platforms.windows;
   };
 }

pkgs/development/libraries/libtheora/mingw-remove-export.patch

@@ -0,0 +1,18 @@
+diff --git a/win32/xmingw32/libtheoradec-all.def b/win32/xmingw32/libtheoradec-all.def
+index 566eeb3..4a2e766 100644
+--- a/win32/xmingw32/libtheoradec-all.def
++++ b/win32/xmingw32/libtheoradec-all.def
+@@ -1,4 +1,3 @@
+-EXPORTS
+ ; Old alpha API
+ 	theora_version_string @ 1
+ 	theora_version_number @ 2
+diff --git a/win32/xmingw32/libtheoraenc-all.def b/win32/xmingw32/libtheoraenc-all.def
+index 36d2dad..d1da2f4 100644
+--- a/win32/xmingw32/libtheoraenc-all.def
++++ b/win32/xmingw32/libtheoraenc-all.def
+@@ -1,4 +1,3 @@
+-EXPORTS
+ ; Old alpha API
+ 	theora_encode_init @ 1
+ 	theora_encode_YUVin @ 2