avoid unneeded source BC_API definitions.
avoid unneeded source BC_API definitions.

Airbitz/libbitcoin,swansontec/libbitcoin,libmetrocoin/libmetrocoin-consensus,GroestlCoin/libgroestlcoin,swansontec/libbitcoin,libmetrocoin/libmetrocoin-consensus,libmetrocoin/libmetrocoin-consensus,libmetrocoin/libmetrocoin-consensus,libtetcoin/libtetcoin-consensus,libtetcoin/libtetcoin-consensus,GroestlCoin/libgroestlcoin,Airbitz/libbitcoin,swansontec/libbitcoin,Airbitz/libbitcoin,Airbitz/libbitcoin,libmetrocoin/libmetrocoin-consensus,libtetcoin/libtetcoin-consensus,libtetcoin/libtetcoin-consensus,GroestlCoin/libgroestlcoin,swansontec/libbitcoin,libtetcoin/libtetcoin-consensus,GroestlCoin/libgroestlcoin