gcc -I. -I. -I/usr/local/rvm/rubies/ruby-1.8.7-p371/lib/ruby/1.8/x86_64-linux -I. -DRUBY_EXTCONF_H=\"extconf.h\"    -fPIC -g -O2  -fPIC     -c domain.c
domain.c:25:21: error: ruby/st.h: No such file or directory
make: *** [domain.o] Error 1

Gem files will remain installed in /usr/local/rvm/gems/ruby-1.8.7-p371@test_develop_pull_request-1/gems/ruby-libvirt-0.5.0 for inspection.
Results logged to /usr/local/rvm/gems/ruby-1.8.7-p371@test_develop_pull_request-1/gems/ruby-libvirt-0.5.0/ext/libvirt/gem_make.out
An error occurred while installing ruby-libvirt (0.5.0), and Bundler cannot
continue.
Make sure that `gem install ruby-libvirt -v '0.5.0'` succeeds before bundling.

See https://www.redhat.com/archives/libvir-list/2013-December/msg00593.html for more info, a 0.5.1 release is coming.