sci-mathematics/gmp-ecm: new EAPI=7 revision.
The dependencies and build system of gmp-ecm have been improved over
the years, and much of the cruft in the ebuild could simply be
deleted. This commit adds an -r2, based on François Bissey's ebuild in
the sage-on-gentoo overlay, to modernize things. I've manually verified
the diff for sanity, and the test suite passes for me on amd64.
Closes: https://bugs.gentoo.org/466498
Package-Manager: Portage-2.3.84, Repoman-2.3.20
Signed-off-by: Michael Orlitzky <mjo@gentoo.org>