Fixed issue where the wrong ImageMagick installation would be used

After installing ImageMagick from MacPorts with FreeType support the
text would become blurry on the icon. The reason was that Xcode would
use another version of ImageMagick in /usr/local/lib which didn’t have
free type support building. The user could see this in the build log by
having several: convert: delegatelibrarysupportnotbuiltin ´none´
(freetype) errors.