compiletest: Run the lldb_batchmode.py script in LLDB's embedded Python

[Zalathar]

Historically, LLDB debuginfo tests have used a Python script to control LLDB via its Python API, instead of invoking the lldb command directly.

Unfortunately, this requires us to find and use a version of Python that is compatible with LLDB's Python bindings.

However, it turns out that there is a simpler way to find a compatible Python interpreter: use the one that is embedded in LLDB itself, via the script command.

[rustbot]

This PR modifies bootstrap.example.toml.

If appropriate, please update CONFIG_CHANGE_HISTORY in src/bootstrap/src/utils/change_tracker.rs.

Some changes occurred in src/tools/compiletest

cc @jieyouxu

[rustbot]

r? @Mark-Simulacrum

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[Zalathar]

Big thanks to @Walnut356 for suggesting the use of LLDB's embedded Python.

cc @jieyouxu @xSetech

This may be a useful alternative to some of the changes proposed in:

• bootstrap: respect build.python on macOS #148636
• compiletest: don't pickup a Python from PYTHONPATH in debuginfo #148646

r? jieyouxu

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[jieyouxu]

@bors try jobs=aarch64-apple

[rust-bors]

☀️ Try build successful (CI)
Build commit: 9d85981 (9d85981868d8787740cfbd23500af90eabf8b01e, parent: 4e0baae06da3c29210ba3620db5b01bcb5aba38a)

[Zalathar]

Pushed a small tweak to explicitly specify that the script is in Python, and not some other language.

Doesn't seem to be needed in practice, but perhaps it will avoid headaches someday.