[perl #126942] [BUG] large right-shift of negative loses sign

[Zoffix Znet via RT]

Thanks for the report. This is now fixed.

Fix:
    https://github.com/MoarVM/MoarVM/commit/362277b79f
    https://github.com/perl6/nqp/commit/9763728215
    https://github.com/rakudo/rakudo/commit/66e8e72c02
    https://github.com/rakudo/rakudo/commit/ef29bb9f41

Tests:
    https://github.com/perl6/roast/commit/02d1f9d0f6
    https://github.com/rakudo/rakudo/commit/6409ee582e