Add xa package

Add pre-built binaries

packages/xa.rb

+require 'package'
+
+class Xa < Package
+  description 'xa is a high-speed, two-pass portable cross-assembler.'
+  homepage 'https://www.floodgap.com/retrotech/xa/'
+  version '2.3.11'
+  compatibility 'all'
+  source_url 'https://www.floodgap.com/retrotech/xa/dists/xa-2.3.11.tar.gz'
+  source_sha256 '32f2164c99e305218e992970856dd8e2309b5cb6ac4758d7b2afe3bfebc9012d'
+
+  binary_url ({
+    aarch64: 'https://dl.bintray.com/chromebrew/chromebrew/xa-2.3.11-chromeos-armv7l.tar.xz',
+     armv7l: 'https://dl.bintray.com/chromebrew/chromebrew/xa-2.3.11-chromeos-armv7l.tar.xz',
+       i686: 'https://dl.bintray.com/chromebrew/chromebrew/xa-2.3.11-chromeos-i686.tar.xz',
+     x86_64: 'https://dl.bintray.com/chromebrew/chromebrew/xa-2.3.11-chromeos-x86_64.tar.xz',
+  })
+  binary_sha256 ({
+    aarch64: '4e9da9aa44ec5d58c597d5f3fcbba2ba3786002e0da6adebe381c4c70f90cda6',
+     armv7l: '4e9da9aa44ec5d58c597d5f3fcbba2ba3786002e0da6adebe381c4c70f90cda6',
+       i686: '9b60a965368eb960b9d06fd80c47be53e30b3a622c966b20a0f7eb04ae051e70',
+     x86_64: '8ea3b2dd25b9b6af9401c653e84ea67c1ba7ce2228d9d8e83d6ab8e3732893d7',
+  })
+
+  def self.patch
+    system "sed -i 's,DESTDIR = /usr/local,DESTDIR = #{CREW_DEST_PREFIX},' Makefile"
+  end
+
+  def self.build
+    system 'make'
+  end
+
+  def self.install
+    system 'make', 'install'
+  end
+end