Cloned from arm-tdep.c, committed per the mult-arch rule.

        * alpha-tdep.c (alpha_abi_handler): New structure to describe
        an Alpha ABI variant. 
        (alpha_abi_handler_list): Declare. 
        (alpha_gdbarch_register_os_abi): New function.
        (alpha_gdbarch_init): Give registered ABI variant handlers a
        chance to tweak the gdbarch once we have set up defaults.
        * alpha-tdep.h: Prototype alpha_gdbarch_register_os_abi.

-- 
        -- Jason R. Thorpe <thorpej@wasabisystems.com>