csu:notes (master)$ gem install gollum-site
Building native extensions. This could take a while...
ERROR: Error installing gollum-site:
ERROR: Failed to build gem native extension.
/Users/christophersu/.rbenv/versions/2.1.5/bin/ruby extconf.rb
checking for ffi.h... no
checking for ffi.h in /usr/local/include... no
checking for rb_thread_blocking_region()... yes
checking for ruby_native_thread_p()... yes
checking for rb_thread_call_with_gvl()... yes
creating extconf.h
creating Makefile
make "DESTDIR=" clean
make "DESTDIR="
Configuring libffi
/bin/sh: ..//Users/christophersu/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/ffi-1.0.12.rc3/ext/ffi_c/libffi/configure: No such file or directory
make: *** ["/Users/christophersu/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/ffi-1.0.12.rc3/ext/ffi_c/libffi"/.libs/libffi_convenience.a] Error 127
make failed, exit code 2
Gem files will remain installed in /Users/christophersu/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/ffi-1.0.12.rc3 for inspection.
Results logged to /Users/christophersu/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/extensions/x86_64-darwin-14/2.1.0-static/ffi-1.0.12.rc3/gem_make.out
csu:notes (master)$ ruby -v
ruby 2.1.5p273 (2014-11-13 revision 48405) [x86_64-darwin14.0]
csu:notes (master)$