(override_options): Handle VAX format floating-point.

(print_operand, case ',', '-'): New cases.
(alpha_builtin_saveregs): Handle VMS convention.
(alpha_sa_{mask,size}, alpha_pv_save_size, alpha_using_fp):
New versions for VMS.
(output_{pro,epi}logue, function_arg): Likewise.
(direct_return): Never true on VMS.
(check_float_value): Return 0 for VMS.
(vmskrunch, alpha_{need,write}_linkage): New function.

From-SVN: r13183