libntl binaries not portable

[E. Madison Bray]

Hello,

(and attn: Marco Atzeri)

I use Cygwin's libntl package in my software, and some users are
reporting illegal instruction errors which appear to be coming from
Cygwin's NTL, which was built with native optimizations enabled.

It should probably be configured with

./configure NATIVE=off

while possibly still selecting at least some arch-specific
optimizations, such as CXXFLAGS=-mavx.

I haven't figured out exactly which features these users' CPUs are
missing but I've seen problems in the past with the PCLMUL
instructions.

Thanks,
Madison