def set_archflags_for_osx
      archflags = []
      fullpath = `which convert`
      fileinfo = `file #{fullpath}`

      # default ARCHFLAGS
      archs = $ARCH_FLAG.scan(/-arch\s+(\S+)/).flatten

      archs.each do |arch|
        archflags << "-arch #{arch}" if fileinfo.include?(arch)
      end

      $ARCH_FLAG = archflags.join(' ') unless archflags.empty?
    end
def set_archflags_for_osx
      archflags = []
      fullpath = `which convert`
      fileinfo = `file #{fullpath}`

      # default ARCHFLAGS
      archs = $ARCH_FLAG.scan(/-arch\s+(\S+)/).flatten

      archs.each do |arch|
        archflags << "-arch #{arch}" if fileinfo.include?(arch)
      end

      $ARCH_FLAG = archflags.join(' ') unless archflags.empty?
    end
issue #169
 set ARCHFLAGS appropriately for OSX