DebugTools: fix linking on Windows.

MSVC complained about dllexporting already exported interface or what.
MinGW doesn't care.

src/DebugTools/ResourceManager.cpp

@@ -35,7 +35,11 @@
 
 namespace Magnum {
 
+#ifndef _WIN32
 template class ResourceManager<AbstractShaderProgram, Buffer, Mesh, MeshView, DebugTools::ForceRendererOptions, DebugTools::ObjectRendererOptions, DebugTools::ShapeRendererOptions>;
+#else
+template class MAGNUM_DEBUGTOOLS_EXPORT ResourceManager<AbstractShaderProgram, Buffer, Mesh, MeshView, DebugTools::ForceRendererOptions, DebugTools::ObjectRendererOptions, DebugTools::ShapeRendererOptions>;
+#endif
 
 namespace DebugTools {
 

src/DebugTools/ResourceManager.h

@@ -45,7 +45,11 @@ namespace Magnum {
 
 /** @todo Do the listing in one place, not five thousand! */
 
+#ifndef _WIN32
 extern template ResourceManager<AbstractShaderProgram, Buffer, Mesh, MeshView, DebugTools::ForceRendererOptions, DebugTools::ObjectRendererOptions, DebugTools::ShapeRendererOptions> MAGNUM_DEBUGTOOLS_EXPORT *& ResourceManager<AbstractShaderProgram, Buffer, Mesh, MeshView, DebugTools::ForceRendererOptions, DebugTools::ObjectRendererOptions, DebugTools::ShapeRendererOptions>::internalInstance();
+#else
+extern template class MAGNUM_DEBUGTOOLS_EXPORT ResourceManager<AbstractShaderProgram, Buffer, Mesh, MeshView, DebugTools::ForceRendererOptions, DebugTools::ObjectRendererOptions, DebugTools::ShapeRendererOptions>;
+#endif
 
 namespace DebugTools {