[lldb] Make TestFormatters.py not rely on working constructor calls

All calls to operator new in this test fail for me with:
```
expression --show-types -- *(new foo(47))`
Error output:
error: Execution was interrupted, reason: internal c++ exception breakpoint(-6)..
The process has been returned to the state before expression evaluation.
```

As calling operator new isn't the idea of this test, this patch moves that
logic to the binary with some new_* utility functions and explicitly tests
this logic in the constructor test (where we can isolate the failures and
skip them on Linux).