Now that ChangeLog entries are no longer used for sim patches,
this commit renames all relevant sim ChangeLog to ChangeLog-2021,
similar to what we would do in the context of the "Start of New
Year" procedure.
The purpose of this change is to avoid people merging ChangeLog
entries by mistake when applying existing commits that they are
currently working on.
Also throw in a .gitignore entry to keep people from adding new
ChangeLog files anywhere in the sim tree.
This is needed to move to automake & its dejagnu-provided logic,
and eventually by the unified sim logic. The $arch is used only
to figure out which `run` program to use when running tests, and
as we move to a single top-level build, we can delete this and
use sim/run directly.
This is a hand-written implementation that should have fairly complete
coverage for the base integer instruction set ("i"), and for the atomic
("a") and integer multiplication+division ("m") extensions. It also
covers 32-bit & 64-bit targets.
The unittest coverage is a bit weak atm, but should get better.
