Adds arch dependent include dir to LIBMAGICK(CORE|WAND)_INCLUDE_DIRS

The last version uploaded in debian has some arch dependent include dirs.
Without them, the compilation fails with a message like:

 fatal error: magick/magick-baseconfig.h: No such file or directory

See:
 https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=747907
 http://www.cmake.org/Bug/view.php?id=15007