From Wang Rui, "I also did a small fix to the ObjectWrapper header, to add a

OSGDB_EXPORT macro to RegisterCompressorProxy, and modified the
findCompressor() method to look for custom compressors in libraries
such like osgdb_compressor_name.so, which was described in the wiki
page chapter 2.4."

include/osgDB/ObjectWrapper

@@ -139,7 +139,7 @@ protected:
     typedef CLASS MyClass; \
     void wrapper_propfunc_##NAME(osgDB::ObjectWrapper* wrapper)
 
-class RegisterCompressorProxy
+class OSGDB_EXPORT RegisterCompressorProxy
 {
 public:
     RegisterCompressorProxy( const std::string& name, BaseCompressor* compressor );