Adds support for restoring the destination mask in the AVX2 gather emulation sequence. As before, detection is done by a state machine that attempts to match a known pattern of the emulation sequence.
Removes the relevant error from client.drx-scattergather and fixes a bug in the test for AVX2 gather in 32-bit mode.
Fixes a bug in the AVX-512 state machine if index is OPSZ_8. Only OPSZ_4 is currently tested in drx.scattergather.
Issue: #2985 (closed)