Prefer lldb over gdb if both are available

Looks like the lldb infrastructure is in a better shape. We should pick up the lldb binary when possible. Currently I get: 
```
which lldb-19 
/usr/bin/lldb-19

idd -c="lldb-19" -ba="/build/vvassilev/llvm-project-17-debug-clad/bin/clang-17" -ra="/build/vvassilev/llvm-project-17-debug-clad/bin/clang-17"
Invalid comparator set
```