Re-instate TARGET_OS=linux in configure.ac. Removed by 351abf9e035.
Re-instate TARGET_OS=linux in configure.ac. Removed by 351abf9e035.

OpenNetworking/gcoin-community,OpenNetworking/gcoin-community,OpenNetworking/gcoin-community,OpenNetworking/gcoin-community,OpenNetworking/gcoin-community,OpenNetworking/gcoin-community,OpenNetworking/gcoin-community