debuginfo tests should detect a python-less gdb

[tromey]

Some of the debuginfo tests require a Python-enabled gdb. If this isn't available, they should be disabled. See rust-lang/rustc-dev-guide#243 and #52452

[Enselic]

Triage: I'm pretty sure Python is mandatory for all tests now? We only support our rust-gdb wrapper and that one requires Python. Closing as obsolete.