There are TONS of these on stackoverflow, all of them recommending more or less the same solution (specify a value for --with-gcc option), but all with conflicting ideas of what exactly to do, and none of them containing a solution that works for the latest version of xcode on mountain lion (I eventually worked out I needed --with-gcc=gcc)
I wonder if someone with greater editorial rights than me would consider it worthwhile compiling all this noise into a post that attempts to explain how to configure rvm for use with different osx/xcode/ruby versions.
- xcodebuild not finding gcc 4.2
- Can't install Ruby under Lion with RVM – GCC issues
- Cannot compile ruby 1.9.3
- Can't compile 1.9.3 with rvm using gcc
- make error when installing `ruby-1.8.7-p334` with `rvm` on Snow Leopard
- Error running make when installing Ruby 1.8.7-p302 via RVM on Mac OS 10.5.8
- Using make on OSX
- How do you install (build) Ruby 1.9.3 on OSX Lion?
- RVM ruby installation errors - Mac