Better system detection for ATLAS.
New archdefs for Cygwin 64 and Raspberry Pi.
Merge remote-tracking branch 'trac/develop' into ticket/14605
Fix autotools optional spkg checksum spurious change.
Trac #14605: Better system detection for ATLAS

See lots of rants in #10508.

This fixes a bunch of problems with ATLAS detection system.
Adds support for (some) ARM hard float systems.
Adds archdefs for Raspberry Pi and Cygwin64.

Use tarball at:
* http://boxen.math.washington.edu/home/jpflori/upstream/atlas-3.10.1.20
140210.tar.bz2

URL: http://trac.sagemath.org/14605
Reported by: jpflori
Ticket author(s): Jean-Pierre Flori
Reviewer(s): Volker Braun