Auto merge of #148685 - Zalathar:lldb-python, r=jieyouxu

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

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.

Author: bors