Instead of just a trivial pad being on or off, support a tri-state
on/off/auto where on will always pad, off will never pad, and auto will
pad only if code caching is enabled.
Further augment this by allowing a byte-width to be passed in, which can
be used with pointers to force a 48-bit VA width to only ever pad to
three instructions, reducing the common worst-case situation from 4
instructions to 3. This works because we're not going to expose a VA
width larger than 47-bit to the guest.
Fixes the handful of use-cases that explicitly chose their NOP padding,
and a bug in Arm64Relocations.cpp where it was incorrectly asking to not
receive padding even though it requires it.
Saves power and responds faster. Pass in the atomic to `WaitPred` with
the predicate checking if the buffer has been flushed yet. Same
behaviour as previous code but more efficient on our hardware.
Billy Laws