RFC: compile with BWX thus only support EV56 and later CPUs

[Michael Cree <mcree@orcon.net.nz>]

There is a discussion on the Linux kernel mailing list that the
kernel in future will only support architectures that can guarantee
atomic aligned scalar accesses down to the byte level (at the moment
the requirement is only for int (32bit) and long (64bit)).  The only
architecture that does not meet this new requirement is older Alphas
that do not have the byte-word extension (BWX) CPU instructions, that
is, EV4, EV45 and EV5. Thus the writing is on the wall that there
will be no more Linux kernels for these older Alphas.

It is also notable that the X server has not worked on these older
Alphas for a number of years.

Furthermore, I estimate that a majority of the bugs I have fixed in
the Debian Alpha distribution over the last couple of years could have
been fixed by compiling with the BWX.  That is, there is growing
bitrot in the non-BWX support in the toolchain.

I therefore propose that we switch the all compilers in Debian-Alpha
to start compiling with the BWX, that is, we henceforth only support
EV56 and later CPUs.  That will provide two primary benefits: more
efficient code and fewer bugs to fix.

I have been giving consideration to giving up maintaining the Alpha
port as soon as Jessie is released because of the amount of work in
keeping the toolchain working.  Dropping non-BWX support might just
tip the balance for me to continue working on Alpha for a bit longer.

Thoughts?  Objections to my proposal?

Cheers
Michael.