Ensure lib-prefix in static MinGW build. Closes #223.

Source/Engine/CMakeLists.txt

@@ -120,7 +120,7 @@ if (APPLE)
     set (FORCE_LOAD -force_load)
 elseif (NOT MSVC)
     set_property (TARGET ${TARGET_NAME} APPEND PROPERTY LINK_LIBRARIES -Wl,--whole-archive)
-    if (WIN32)
+    if (WIN32 AND URHO3D_LIB_TYPE STREQUAL SHARED)
         set_target_properties (${TARGET_NAME} PROPERTIES PREFIX "")
     endif ()
 endif ()