BUG: fix mingw module load tests

Modules/Platform/Windows-gcc.cmake

@@ -3,7 +3,6 @@ SET(CMAKE_STATIC_LIBRARY_PREFIX "lib")
 SET(CMAKE_STATIC_LIBRARY_SUFFIX ".a")
 SET(CMAKE_SHARED_LIBRARY_PREFIX "lib")          # lib
 SET(CMAKE_SHARED_LIBRARY_SUFFIX ".dll")          # .so
-SET(CMAKE_SHARED_MODULE_PREFIX "")
 SET(CMAKE_DL_LIBS "")
 SET(CMAKE_SHARED_LIBRARY_C_FLAGS "")            # -pic 
 SET(CMAKE_SHARED_LIBRARY_CREATE_C_FLAGS "-shared")       # -shared

Source/cmDynamicLoader.cxx

@@ -274,7 +274,11 @@ cmDynamicLoader::GetSymbolAddress(cmLibHandle lib, const char* sym)
 
 const char* cmDynamicLoader::LibPrefix()
 { 
+#if defined( __MINGW32__ )
+  return "lib";
+#else
   return "";
+#endif
 }
 
 const char* cmDynamicLoader::LibExtension()