Building native extensions. This could take a while...
ERROR: Error installing rmagick:
ERROR: Failed to build gem native extension.
/usr/bin/ruby extconf.rb
checking for gcc... yes
checking for Magick-config... no
checking for pkg-config... yes
...
Gem files will remain installed in /usr/local/share/gems/gems/rmagick-2.15.4 for inspection.
Results logged to /usr/local/share/gems/gems/rmagick-2.15.4/ext/RMagick/gem_make.out