Add giflib package

Add pre-built binaries

packages/giflib.rb

+require 'package'
+
+class Giflib < Package
+  description 'giflib is a library for reading and writing gif images.'
+  homepage 'http://giflib.sourceforge.net/'
+  version '5.1.4'
+  source_url 'https://prdownloads.sourceforge.net/project/giflib/giflib-5.1.4.tar.bz2'
+  source_sha256 'df27ec3ff24671f80b29e6ab1c4971059c14ac3db95406884fc26574631ba8d5'
+
+  binary_url ({
+    aarch64: 'https://dl.bintray.com/chromebrew/chromebrew/giflib-5.1.4-chromeos-armv7l.tar.xz',
+     armv7l: 'https://dl.bintray.com/chromebrew/chromebrew/giflib-5.1.4-chromeos-armv7l.tar.xz',
+       i686: 'https://dl.bintray.com/chromebrew/chromebrew/giflib-5.1.4-chromeos-i686.tar.xz',
+     x86_64: 'https://dl.bintray.com/chromebrew/chromebrew/giflib-5.1.4-chromeos-x86_64.tar.xz',
+  })
+  binary_sha256 ({
+    aarch64: '546af3350ca70ffc33ba0c12e6de65efe2fc9bce95ef3c48ab81da2d6cc1cae0',
+     armv7l: '546af3350ca70ffc33ba0c12e6de65efe2fc9bce95ef3c48ab81da2d6cc1cae0',
+       i686: 'ad9b824becceb46ad8b22515085ea105497117e10e7550f7ba965398c4d56d36',
+     x86_64: '2efb3d4ac43bd4400e5af45cf8281e1852b86a2050af1efb0437eb9e92cd3312',
+  })
+
+  def self.build
+    system './configure',
+           "--prefix=#{CREW_PREFIX}",
+           "--libdir=#{CREW_LIB_PREFIX}",
+           '--disable-dependency-tracking'
+    system 'make'
+  end
+
+  def self.check
+    system 'make', 'check'
+  end
+
+  def self.install
+    system 'make', "DESTDIR=#{CREW_DEST_DIR}", 'install'
+  end
+end