set SDLMIXER_VENDORED to ON and vendor the required libraries into libs/SDL3_mixer/external

disable SDLMIXER_VORBIS_VORBISFILE
add ogg v1.3.5-SDL
add opus v1.4.x-SDL
add opusfile v0.13-git-SDL

libs/SDL3_mixer/external/ogg/appveyor.yml

@@ -0,0 +1,33 @@
+image: Visual Studio 2015
+configuration:
+- Debug
+- Release
+
+platform:
+- Win32
+- x64
+
+environment:
+  matrix:
+  - BUILD_SYSTEM: MSVC
+  - BUILD_SYSTEM: CMAKE
+
+build_script:
+  - if "%BUILD_SYSTEM%" == "MSVC" (
+      msbuild "%APPVEYOR_BUILD_FOLDER%\win32\VS2015\libogg.sln" /m /v:minimal /logger:"C:\Program Files\AppVeyor\BuildAgent\Appveyor.MSBuildLogger.dll" /property:Configuration=%CONFIGURATION%;Platform=%PLATFORM%
+    )
+  - if "%BUILD_SYSTEM%" == "CMAKE" (
+      mkdir "%APPVEYOR_BUILD_FOLDER%\build" &&
+      pushd "%APPVEYOR_BUILD_FOLDER%\build" &&
+      cmake -A "%PLATFORM%" -G "Visual Studio 14 2015" .. &&
+      cmake --build . --config "%CONFIGURATION%" -- /logger:"C:\Program Files\AppVeyor\BuildAgent\Appveyor.MSBuildLogger.dll" &&
+      popd
+    )
+
+after_build:
+  - if "%BUILD_SYSTEM%" == "MSVC" (
+      7z a ogg.zip win32\VS2015\%PLATFORM%\%CONFIGURATION%\libogg.lib include\ogg\*.h
+    )
+
+artifacts:
+- path: ogg.zip