The issue is with Lion, and I've encountered this myself on now 2 brand-new 13-inch MBP's.
What you need to do is install the OSX GCC Compilers separately.
They can be found here: https://github.com/kennethreitz/osx-gcc-installer (scroll down to downloading pre-build binaries)
After downloading and running through the package installer (you should not need to install Homebrew), you need to find where the GCC folder is located. For some people, it was in /usr/bin
; however, for me I found it in /Developer/usr/bin
Add this directory to your $PATH variable in your ~/.profile
or ~/.bash_profile
file. For me, I'm using ~/.bash_profile
and added it to the end using vim.
Close your Terminal and open it again, and then echo $PATH
to make sure the changes saved.
Completely uninstall that version of ruby, and install again normally:
rvm install 1.8.7
rvm use 1.8.7
If it still doesn't work, I recommend installing your version of rails using the following command as Hans specified in Why can't I install Rails on Lion using RVM?:
CC=/usr/bin/gcc-4.2 rvm install ruby-1.8.7 --force
the CC directory would change based on where your install was. However, after adding the correct path to gcc to my $PATH variable, I did not need to do the above command.
If you were still having this problem, hope this helps.