dev-lang/moarvm: Fix dependency on libtommath-1.0 re bugs #608548 and #576284

dev-lang/moarvm: Fix dependency on libtommath-1.0 re bugs #608548 and #576284

Upstream has used a bundled copy of libtommath at version 1.0 since
version 2016.02, but we use system copies, and so, which end users
who are running full ~arch would have gotten a working version by
fortunate accident.

An -r1 bump is required here, as dependency propagation must replicate,
even for people who already have compile working, as users must be
discouraged fron downgrading libtommath if they try to do partial
reversion to 'arch'

Thanks to the patient reporters and commenters on the related bugs.

Bug: https://bugs.gentoo.org/576284
Bug: https://bugs.gentoo.org/608548
Package-Manager: Portage-2.3.6, Repoman-2.3.2