Unfortunately, it seems that by adding $ CFLAGS="-03" CXXFLAGS="-03" to ./install.sh ... the compilation stops at:
configure:3495: error: in `/home/user11/gitprojects2/libbitcoin4/build-libbitcoin-node/secp256k1':
configure:3497: error: C compiler cannot create executables
See `config.log' for more details
