Changes for GMP 6.1.2

[Torbjörn Granlund]

"Marco Bodrato" <bodrato at mail.dm.unipi.it> writes:

  I hope I did it correctly.
  
The testing run from last night seems happy.

I needed to make fairly large changes to the configure stuff for arm
since the old code caused problems for several CPUs.  I merged the
needed changes from the head repo, and also brought over ppc
improvements.

I hope to add some new x86 CPUs to config.guess before the release
(mainly any missing Intel Kaby Lake and AMD Zen).

Making the release around the 15th would be good.

-- 
Torbjörn
Please encrypt, key id 0xC8601622