Installing rmagick 2.13.1 with graphicsmagick on Ubuntu 10.04

I previously had an rmagick gem installation that works with ImageMagick. ImageMagick was installed from source with OpenMP disabled. This installation works without a hitch. However I attempted to uninstall rmagick and ImageMagick so that I could have a version that works with GraphicsMagick.

So I installed GraphicsMagick from source and disabled OpenMP feature once again. However, When I install rmagick I get the following:

Building native extensions.  This could take a while...
ERROR:  Error installing rmagick-2.13.1.gem:
        ERROR: Failed to build gem native extension.

        /usr/bin/ruby1.8 extconf.rb --build-opts --with-graphics-magick
checking for Ruby version >= 1.8.5... yes
checking for gcc... yes
checking for Magick-config... yes

Warning: Found a partial ImageMagick installation. Your operating system likely has some built-in ImageMagick libraries but not all of ImageMagick. This will most likely cause problems at both compile and runtime.
Found partial installation at: /usr
checking for ImageMagick version >= 6.4.9... yes
checking for HDRI disabled version of ImageMagick... yes
Package MagickCore was not found in the pkg-config search path.
Perhaps you should add the directory containing `MagickCore.pc'
to the PKG_CONFIG_PATH environment variable
No package 'MagickCore' found
Package MagickCore was not found in the pkg-config search path.
Perhaps you should add the directory containing `MagickCore.pc'
to the PKG_CONFIG_PATH environment variable
No package 'MagickCore' found
Package MagickCore was not found in the pkg-config search path.
Perhaps you should add the directory containing `MagickCore.pc'
to the PKG_CONFIG_PATH environment variable
No package 'MagickCore' found
Package MagickCore was not found in the pkg-config search path.
Perhaps you should add the directory containing `MagickCore.pc'
to the PKG_CONFIG_PATH environment variable
No package 'MagickCore' found
checking for stdint.h... yes
checking for sys