$zero on alpha should always be available

[Joel Brobecker]

> Here's what I came up with by inspection.  I have no alpha machine to test
> this on.  The alpha-nat.c change would need
> checking on an alpha running OSF if we wanted to test this...

Thanks, Pedro.  I will try to test this tomorrow. I think Tru64 is
one of the systems where expect or tcl no longer work for me, so
I might not be able to run the testsuite. But worse case scenario,
I can try running it against AdaCore's testsuite.

> 2011-05-23  Pedro Alves  <pedro@codesourcery.com>
> 
> 	gdb/
> 	* alpha-tdep.c (alpha_cannot_fetch_register): Don't return true
> 	for ALPHA_ZERO_REGNUM.
> 	(alpha_supply_int_regs): Explicitly supply zero as the value for
> 	ALPHA_ZERO_REGNUM in the register cache.
> 	* alpha-nat.c (fetch_osf_core_registers): Ditto.

-- 
Joel