[lldb] Refactor TestFixIts so that most of it can run on aarch64-linux

The final function call to `test_X` is failing on aarch64-linux with SIGILL.
Function calls to previous expressions seem to just not work on aarch64-linux
but I don't see another way to test the multiple-run Fix-Its.

This patch refactors the test that the skipIf for aarch64 Linux only covers
the part of the test that was added D77214.