sci-libs/fflas-ffpack: new package for finite-field linear algebra.

sci-libs/fflas-ffpack: new package for finite-field linear algebra.

This is a straightforward import of the latest fflas-ffpack-2.4.3.ebuild
that François Bissey has been maintaining in the sage-on-gentoo overlay,
with only a few minor changes:

  * I added a "+" to the LICENSE to match the upstream LGPL-2.1+.

  * I switched the openmp check to use tc-check-openmp() conditionally
    on the MERGE_TYPE variable.

  * Added BDEPEND="virtual/pkgconfig" since we patch in a call to
    PKG_CHECK_MODULES.

I also removed a warning about build failures with USE=openmp. From what
I can tell, this stems from an older report (upstream Github issue 48)
using gcc-4.9.x that was never fully debugged. If the problems persist,
we can revisit that report, or just mask the flag.

Closes: https://bugs.gentoo.org/show_bug.cgi?id=715678
Package-Manager: Portage-2.3.89, Repoman-2.3.20
Signed-off-by: Michael Orlitzky <mjo@gentoo.org>