So we don't expose builders to network flakiness which cannot be worked
around using cargo's --offline flag.

* Using the shared jit crate, support for a single global_allocator can
function
* Solves --zjit-mem-size

* ruby.rs should hold the main entrypoint to YJIT and ZJIT
* The crate jit will hold code shared between them

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.

Bumps [capstone](https://github.com/capstone-rust/capstone-rs) from 0.12.0 to 0.13.0.
- [Release notes](https://github.com/capstone-rust/capstone-rs/releases)
- [Changelog](https://github.com/capstone-rust/capstone-rs/blob/master/CHANGELOG.md)
- [Commits](https://github.com/capstone-rust/capstone-rs/compare/capstone-v0.12.0...capstone-v0.13.0)

---
updated-dependencies:
- dependency-name: capstone
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

* YJIT: Allow dev_nodebug to disasm release-mode code

* Revert "YJIT: Squash canary before falling back"

This reverts commit f05ad373d84909da7541bd6d6ace38b48eaf24a1.
The stray canary issue should have been solved by
def7023ee4a3fc6eeba9d3a34c31a5bcff315fac, alleviating this codegen
accommodation.

* s/runtime_assertions/runtime_checks/

---------

Co-authored-by: Alan Wu <XrXr@users.noreply.github.com>

Bumps [capstone](https://github.com/capstone-rust/capstone-rs) from 0.11.0 to 0.12.0.
- [Release notes](https://github.com/capstone-rust/capstone-rs/releases)
- [Changelog](https://github.com/capstone-rust/capstone-rs/blob/master/CHANGELOG.md)
- [Commits](https://github.com/capstone-rust/capstone-rs/compare/capstone-v0.11.0...capstone-v0.12.0)

---
updated-dependencies:
- dependency-name: capstone
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Bumps [capstone](https://github.com/capstone-rust/capstone-rs) from 0.10.0 to 0.11.0.
- [Release notes](https://github.com/capstone-rust/capstone-rs/releases)
- [Changelog](https://github.com/capstone-rust/capstone-rs/blob/master/CHANGELOG.md)
- [Commits](https://github.com/capstone-rust/capstone-rs/compare/capstone-v0.10.0...capstone-v0.11.0)

---
updated-dependencies:
- dependency-name: capstone
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>