Remove obsolete Tru64 UNIX V5.1B support

[Douglas Rupp]

On 3/5/2012 9:28 AM, Richard Henderson wrote:
> On 03/05/2012 09:14 AM, Rainer Orth wrote:
>> * In the alpha backend, there are a couple of cases that might be
>>    osf-specific, but I cannot tell for certain:
>>
>>    macro				  osf5.h        alpha.h
>>
>>    TARGET_AS_CAN_SUBTRACT_LABELS	  1		TARGET_GAS
>>
>>    I cannot tell if !TARGET_GAS configurations exist, especially Alpha VMS.
>>    Also, in alpha.h there are some references to mips-tfile, which is
>>    gone with osf.  If there are no non-gas configrations remaining, that
>>    stuff can go, too.
> Given that GAS supports VMS, I suspect that all targets are now GAS.
> I'll let the adacore folks answer that for certain howeverl.
>
All Alpha/VMS targets use GAS.
--Doug