#ifdef PERL_INC_VERSION_LIST *is* true if it's set to something like "5.10.10",0 in Config.h - and that happens when the changes to config_H.gc and config.gc (mentioned above) are made. Without those changes, however, PERL_INC_VERSION_LIST will *not* be defined in Config.h.
Also, the directory /perl/site/5.10.0/lib does exist for me ... there must be other hacks required ...