Added ARCH_ZARCH as architecture option

SystemZ (z/os, mainframe) added as a constant to the arch.rb file.  This
along with other commits in this package will allow for development of
SystemZ (mainframe) based modules.

lib/rex/arch.rb

@@ -18,6 +18,7 @@ module Arch
   #
   require 'rex/arch/x86'
   require 'rex/arch/sparc'
+  require 'rex/arch/zarch'
 
   #
   # This routine adjusts the stack pointer for a given architecture.
@@ -64,6 +65,8 @@ module Arch
         [addr].pack('V')
       when ARCH_ARMBE
         [addr].pack('N')
+      when ARCH_ZARCH
+        [addr].pack('Q>')
     end
   end
 
@@ -95,6 +98,8 @@ module Arch
         return ENDIAN_LITTLE
       when ARCH_ARMBE
         return ENDIAN_BIG
+      when ARCH_ZARCH
+        return ENDIAN_BIG
     end
 
     return ENDIAN_LITTLE