I ran into an issue the other day that was exacerbated by the fact that blog posts on the subject seemed to be out of date. Therefore, this is an attempt to bring a more up-to-date solution.
The other day, I was in the position where I had to recompile Vim (and GVim) on Ubuntu. I had installed the version from aptitude, which is perfectly good apart from the fact that it requires and installs the ruby 1.8.7 package. I actually use RVM for my ruby binary management, and I wanted to tell Vim to use the ruby 1.9.3 installed on my system via RVM.