alpha: half done futex implementation

[Segher Boessenkool]

> Also, there's a bug in the powerpc implementation.  It appears that  
> oparg is clobbered, and if stwcx fails the operation will be  
> repeated with incorrect inputs.

If either the lwarx or the stwcx. faults, the routine returns -EFAULT
and doesn't retry (label "3" is the end of the asm).

If the stwcx. fails because the CPU lost the reservation, %1 isn't
clobbered as far as I see?


Segher