Building libbitcoin libraries on Arch linux fails
Library modules provided by github/libbitcoin (incl. forked version of libsecp256k1) are by default installed using prefix /usr/local. configure script, that is run during build process, however, doesn't by default search for dependencies in /usr/local. So in order to make configure find other modules, one has to change the prefix for each module or tell the configure script where to look for the libraries - e. g. by setting variable PKG_CONFIG_PATH before running the script:
export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig.
pkgconfig directory contains configuration files with all needed information for those affected dependencies, so if the variable is set correctly, configure script will find them and compilation will be successful.

P. S. the compilation of libsecp256k1 needs to be done with flag --enable-module-recovery so as to be compatible with libbitcoin.