GMP performance leap

[Torbjorn Granlund]

I reran GMPbench with current head repo sources and got a surprise.
There is a large leap in performance for AMD K10, and nice improvements
for a lot of other CPUs as well, compared to GMP 5.0.

AMD K10 went from 2985 to 3500 with improvements at every measured
point.

The thing is that I am not sure which changes has made such a great
difference.  Anyway, great work by somebody!

See: http://gmplib.org/gmpbench.html

The one sad part is that K10 is being discontinued, with Bulldozer as
suggested replacement.  Its score is about 660 per GHz, while K10's is
almost 1100...

-- 
Torbjörn