Added test for a particularly convoluted case requiring fixup in
V3Premit. To help with statistics stability, also prevent V3Premit from
introducing temporaries for assignment where the RHS reads the LHS, but
the assignment is known to be atomic (by emitted C++ semantics).
Also rename `createWideTemp` to `createTemp`, as it is used for non-wide
expressions as well.
Geza Lore