fix cmake warning: protobuf patch
fix cmake warning: protobuf patch

top-level project() command
protobuf commit https://github.com/smanders/protobuf/commit/c884d84f34c30915892bc316b1c28395585d1a1d
issue https://github.com/smanders/externpro/issues/274#issuecomment-654472915

smanders/externpro