Set explicit Boost/GMP discovery only if we build Boost/GMP, respectively.
Set explicit Boost/GMP discovery only if we build Boost/GMP, respectively.

libmetrocoin/libmetrocoin-explorer,libtetcoin/libtetcoin-explorer,GroestlCoin/libgroestlcoin-explorer,GroestlCoin/libgroestlcoin-explorer,cancoin/libbitcoin-explorer,libtetcoin/libtetcoin-explorer,libmetrocoin/libmetrocoin-explorer,cancoin/libbitcoin-explorer,tuomassiren/libbitcoin-explorer,tuomassiren/libbitcoin-explorer,GroestlCoin/libgroestlcoin-explorer