[lldb] Fix some tests that fail with system libstdc++ (llvm#106885)

This is a revert of b1fcc18.

These tests weren't working on Ubuntu 22.04 or Fedora 37-40. I'm not
sure exactly why, but it seems like they may be incompatible with
libstdc++. Also, despite the fact that the tests were using the system
libstdc++, the tests were only run when libcxx was enabled.

I tested this with a RelWithDebInfo build and the tests passed.

Fixes llvm#106475

(cherry picked from commit adf44d5)

Author: tstellar