Cannot compile ruby 1.9.3
With Xcode 4.6 I was also getting this problem. I installed the command line tools which made gcc available in /usr/bin/gcc.
I managed to get it to work using:
rvm install 1.9.3 --with-gcc=gccNB. I dont have homebrew installed.
you are using clang, according to this ticket http://bugs.ruby-lang.org/issues/5883 - it's not "fully" supported - you need to try using gcc-4.2, you get instructions for homebrew with running rvm requirements.
here is RVM ticket for this problem https://github.com/wayneeseguin/rvm/issues/1480
UPDATE: Ruby-2.0.0 actually compiles better with clang then with gcc-4.2, more details here: https://stackoverflow.com/a/15655034/497756
If you don't have rvm already installed, rvm requirements won't work. Install gcc 4.2 with homebrew and restart the rvm installation. Worked for me.
brew updatebrew tap homebrew/dupesbrew install apple-gcc42