message: improve macOS-compatibility by being more awful
diff: #!/bin/sh
  set -e
  -TARGET=$(rustc --print target-spec-json -Z unstable-options | jq '.["llvm-target"]' -r)
  +# I'd love to use `jq` for parsing the JSON properly, but macOS is totally underequipped for this kind of work.
  +TARGET=$(rustc --print target-spec-json -Z unstable-options | grep llvm-target | cut -d '"' -f 4)
  SYSROOT=$(rustc --print sysroot)
  # We set the rpath so that Miri finds the private rustc libraries it needs.
  # We enable debug-assertions to get tracing.
  