Add pkg-config to Linux packages
Add pkg-config to Linux packages

libsodium-sys is not building without pkg-config.
And last one is not installed everywhere by default.

Former-commit-id: 036006c0db31c068affb4b4a478289d66b5864e8
exonum/exonum,exonum/exonum,exonum/exonum,alekseysidorov/exonum,exonum/exonum,alekseysidorov/exonum,alekseysidorov/exonum,alekseysidorov/exonum