https://github.com/ruby/mmtk/commit/9876d8f0a1

https://github.com/ruby/mmtk/commit/de252637ec

Remove the unused constant HAS_MOVED_GFIELDSTBL and related methods.

In the mmtk/mmtk-ruby repo, we are now able to find the global field
(IV) table of a moved object during copying GC without using the
HAS_MOVED_GFIELDSTBL bit.  We synchronize some of the code, although we
haven't implemented moving GC in ruby/mmtk, yet.

See: https://github.com/mmtk/mmtk-ruby/commit/13080acdf553f20a88a7ea9ab9f6877611017136

https://github.com/ruby/mmtk/commit/400ba4e747

This commit allows building YJIT and ZJIT simultaneously, a "combo
build". Previously, `./configure --enable-yjit --enable-zjit` failed. At
runtime, though, only one of the two can be enabled at a time.

Add a root Cargo workspace that contains both the yjit and zjit crate.
The common Rust build integration mechanisms are factored out into
defs/jit.mk.

Combo YJIT+ZJIT dev builds are supported; if either JIT uses
`--enable-*=dev`, both of them are built in dev mode.

The combo build requires Cargo, but building one JIT at a time with only
rustc in release build remains supported.

https://github.com/ruby/mmtk/commit/f47a1e2d17

Fixes a bug where there is an infinite loop when MMTK_HEAP_MIN is small.

https://github.com/ruby/mmtk/commit/12c7ede20b

https://github.com/ruby/mmtk/commit/52b857ea04

https://github.com/mmtk/mmtk-core/pull/1261 fixes an issue where the following
script causes a Rust panic:

    GC.disable
    10_000.times { Object.new }
    puts GC.stat

https://github.com/ruby/mmtk/commit/6191ee994a

https://github.com/ruby/mmtk/commit/63ab563e04

https://github.com/ruby/mmtk/commit/68bf1b638263

https://github.com/ruby/mmtk/commit/ba1ec69bf6