Log Message:
Updated lang/racket to version 6.12.

First and foremost, I have added some patches that disable MPROTECT for
some Racket executables and fix PR pkg/53467.

As for changes since the latest version, 6.11, these include:
* Changed the way some unsafe operations are exposed via `ffi/unsafe`
  libraries to help smooth a future transition to a new runtime system.

* The `syntax-parse` form supports unwinding side-effects when it
  backtracks, both explicitly with `~undo` patterns and implicitly
  with the built-in managed state (using `syntax-parse-state-ref`,
  etc).

* The `db` library supports SCRAM-SHA-256 authentication for backends
  running PostgreSQL 10 or later. Client support for SCRAM and other
  SASL mechanisms is provided by the new `sasl` library.

* The `lazy-require-syntax` form supports lazy loading of macro
  transformers. Note that the macros must obey certain implementation
  constraints (see the `lazy-require-syntax` documentation).

* Typed Racket no longer enforces types like `(U String (Boxof String))`
  with the `any/c` contract. This fixes a type soundness issue, but may
  affect performance. Please submit a bug report if you find a program
  that runs significantly slower on v6.12 than earlier versions.

* Typed Racket's type instantiation (`inst`) uses `Any` for omitted type
  arguments, allowing APIs to add additional type variables to functions
  without breaking existing programs.

* `for/fold` users can customize the final result of a loop's computation
  using the `#:result` keyword.

* The `--deps` option to `raco test` tests the packages the argument
  packages depends on, in addition to testing the packages themselves.
  For example, `raco test -p --deps pkg1 pkg2` tests all files from
  `pkg1`, `pkg2`, and all of their dependencies.