(separate bug for root cause of 32bit build break) Looking at Base64.h, there are 4 adapters and 2 actual implementations, but all are marked WTF_EXPORT_PRIVATE. Since EncodedValue.h is included multiple places, it will trigger weak symbol problems that seem to have been latent in that header.
Committed r171696: <http://trac.webkit.org/changeset/171696>