Physics: properly instantiate and export global debugdraw manager instance.

Otherwise it failed at runtime on assertion in instance().

src/Physics/DebugDrawResourceManager.cpp

@@ -13,6 +13,8 @@
     GNU Lesser General Public License version 3 for more details.
 */
 
+#define MAGNUM_RESOURCEMANAGER_DEFINE_INTERNALINSTANCE
+
 #include "DebugDrawResourceManager.h"
 
 #include "AbstractShaderProgram.h"

src/Physics/DebugDrawResourceManager.h

@@ -21,7 +21,12 @@
 
 #include "Magnum.h"
 #include "Color.h"
+
+#ifndef MAGNUM_RESOURCEMANAGER_DEFINE_INTERNALINSTANCE
+#define MAGNUM_RESOURCEMANAGER_DONT_DEFINE_INTERNALINSTANCE
+#endif
 #include "ResourceManager.h"
+
 #include "SceneGraph/SceneGraph.h"
 
 #include "magnumPhysicsVisibility.h"
@@ -41,6 +46,8 @@ namespace Physics { namespace Implementation {
 }}
 #endif
 
+extern template ResourceManager<AbstractShaderProgram, Buffer, Mesh, Physics::Implementation::Options> PHYSICS_EXPORT *& ResourceManager<AbstractShaderProgram, Buffer, Mesh, Physics::Implementation::Options>::internalInstance();
+
 namespace Physics {
 
 template<std::uint8_t> class AbstractShape;