build: fix build of virt-login-shell on systems with older gnutls
build: fix build of virt-login-shell on systems with older gnutls

On systems where gnutls uses libgcrypt, I'm seeing the following
build failure

libvirt.c:314: error: variable 'virTLSThreadImpl' has initializer but incomplete type
libvirt.c:319: error: 'GCRY_THREAD_OPTION_PTHREAD' undeclared here (not in a function)
...

Fix by undefining WITH_GNUTLS_GCRYPT in config-post.h

datto/libvirt,zippy2/libvirt,elmarco/libvirt,fabianfreyer/libvirt,zhlcindy/libvirt-1.1.4-maintain,eskultety/libvirt,taget/libvirt,libvirt/libvirt,agx/libvirt,nertpinx/libvirt,datto/libvirt,nertpinx/libvirt,andreabolognani/libvirt,elmarco/libvirt,rlaager/libvirt,datto/libvirt,datto/libvirt,zhlcindy/libvirt-1.1.4-maintain,andreabolognani/libvirt,taget/libvirt,agx/libvirt,shugaoye/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,cbosdo/libvirt,cbosdo/libvirt,zippy2/libvirt,jfehlig/libvirt,elmarco/libvirt,datto/libvirt,zippy2/libvirt,agx/libvirt,jfehlig/libvirt,jardasgit/libvirt,jardasgit/libvirt,rlaager/libvirt,nertpinx/libvirt,zhlcindy/libvirt-1.1.4-maintain,jfehlig/libvirt,olafhering/libvirt,nertpinx/libvirt,taget/libvirt,taget/libvirt,libvirt/libvirt,eskultety/libvirt,eskultety/libvirt,zippy2/libvirt,rlaager/libvirt,VenkatDatta/libvirt,shugaoye/libvirt,crobinso/libvirt,libvirt/libvirt,VenkatDatta/libvirt,crobinso/libvirt,andreabolognani/libvirt,zhlcindy/libvirt-1.1.4-maintain,nertpinx/libvirt,cbosdo/libvirt,olafhering/libvirt,zhlcindy/libvirt-1.1.4-maintain,elmarco/libvirt,rlaager/libvirt,eskultety/libvirt,andreabolognani/libvirt,shugaoye/libvirt,eskultety/libvirt,agx/libvirt,cbosdo/libvirt,andreabolognani/libvirt,jardasgit/libvirt,agx/libvirt,VenkatDatta/libvirt,jardasgit/libvirt,crobinso/libvirt,shugaoye/libvirt,elmarco/libvirt,cbosdo/libvirt,taget/libvirt,rlaager/libvirt,olafhering/libvirt,fabianfreyer/libvirt,VenkatDatta/libvirt,shugaoye/libvirt,crobinso/libvirt,fabianfreyer/libvirt,libvirt/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,olafhering/libvirt,VenkatDatta/libvirt