Debuginfo tests don't control for ambient tools

[workingjubilee]

The debuginfo tests should probably use a specific debugger, like maybe an lldb we build with the compiler, so that they work consistently. In practice, they have been effectively broken on user's machines by just trying to use whatever is installed.

In other words: just because I use Linux doesn't mean I have gdb installed.

[workingjubilee]

The debuginfo test suite should also be insulated against gdb changing how it prints things, Because It Does.

[Noratrieb]

Some points:

• compiletest supports cdb, gdb and lldb, running the test suite for all the ones that are available (either via config.toml or via PATH).
• our LLVM builds do currently not contain lldb.

[workingjubilee]

That's... informative, thank you!

It does seem like we should reassess our strategy if we're gonna run a test suite that isn't guaranteed to pass even between different versions of a debugger on "any ol' random debugger lying around".

[bjorn3]

On macOS we can't ship our own debugger. Only an Apple signed lldb is allowed to use the debugging apis of the kernel.

[workingjubilee]

Wait, gdb is useless on macOS?