Mac Rmagick won't install with Xcode 4.2
I tried your solution (full of hope) but It did not work for me unfortunately.Finally I managed to make it work by reinstalling imagemagick without openmp support (this is the library responsible for lgomp)
using Homebrew:
brew install imagemagick --disable-openmpthen rmagick installed without any problems.
I tried to download and install 4.1 for lion and this didn't even install (without a proper error message).Now a colleague gave me this great link to GCC for Mac which worked like a charm:https://github.com/kennethreitz/osx-gcc-installer
Don't forget to download the v2 if you run on > 10.7.0
For people who want source installation, you can download the source code repository and issue this command in the imagemagick source code directory.
./configure --disable-openmp
It will work similar to the brew version above but with source code compilation instead.