Installation of libpari.dll.a on Cygwin

[Jean-Pierre Flori <flori@enst.fr>]

Dear all,

When PARI is built on Cygwin, there is a nice .dll.a import file which
is created.
However it is then not installed, only the .dll file is.

Would you consider installing it as well?

I guess it could have two benefits:
- people could use it,
- ld will find the shared version before the static one when both are
installed and so will use it by default when no -static flag is given
(which is the behavior I'd prefer personally).

Best,

-- 
Jean-Pierre Flori