[VIRT-327 # Richard's upstream QEMU work ]

Fix TranslationBlock overflow, launchpad 1824853.

Investigated launchpad 1824768, i386 emulation on arm32. But works-for-me.

A bunch of work on new gvec primitives. Primarily to support David Hildebrand's target/s390 conversion, but it does enable more vectorization in target/arm as well.

r~