TME extension: ideas on how to (ab)use it

[skmp]

Following up from yesterday's discussion,

For tso/non-tso memory tracking, we might be able to group accesses between atomic ops in transactions, and detect concurrent access with transaction aborts. Might get us more precise tracking than the MTE approach.

For synchronous detection of segfaults, we might be able to wrap code between guest abi sync points around a transaction, and on transaction abort execute some slowpath. Details on synchronous signal complications in #1682

TME Extension details: https://developer.arm.com/documentation/101028/0012/16--Transactional-Memory-Extension--TME--intrinsics?lang=en