Only add additional warnings if we have a GNU compiler.
Only add additional warnings if we have a GNU compiler.

jt1/honeypot-libssh,miloj/libssh-v0.5,wangshawn/libssh,sebadoom/libssh,mwgoldsmith/libssh,pouete/libssh,pouete/libssh,bigcat26/libssh-mod,nviennot/libssh,substack/libssh,DouglasHeriot/libssh,taikoo/libssh,mwgoldsmith/ssh,robxu9/libssh,Distrotech/libssh,jahrome/libssh,kedazo/libssh,wangshawn/libssh,sebadoom/libssh,robxu9/libssh,taikoo/libssh,miloj/libssh-v0.5,bigcat26/libssh-mod,jahrome/libssh,jt1/honeypot-libssh,DouglasHeriot/libssh,rofl0r/libssh,Distrotech/libssh,elastichosts/libssh,mwgoldsmith/ssh,miloj/libssh-v0.5,jahrome/libssh,elastichosts/libssh,DouglasHeriot/libssh,miloj/libssh-v0.5,nviennot/libssh,mwgoldsmith/ssh,pouete/libssh,substack/libssh,mwgoldsmith/ssh,bigcat26/libssh-mod,rofl0r/libssh,robxu9/libssh,kedazo/libssh,mwgoldsmith/libssh,mwgoldsmith/libssh,sebadoom/libssh,jt1/honeypot-libssh,Distrotech/libssh,taikoo/libssh,nviennot/libssh,kedazo/libssh,bigcat26/libssh-mod,kedazo/libssh,nviennot/libssh,wangshawn/libssh,substack/libssh,robxu9/libssh,wangshawn/libssh,elastichosts/libssh,taikoo/libssh,substack/libssh,jahrome/libssh,rofl0r/libssh,jt1/honeypot-libssh,sebadoom/libssh,mwgoldsmith/libssh,pouete/libssh,DouglasHeriot/libssh,Distrotech/libssh,rofl0r/libssh