this ensures the compiler doesn't assume that new always returns a
non-NULL value. Without this the compiler may remove the error path in
code like this:
```
MyObject *x = new MyObject;
if (x == nullptr) {
::printf("Alloc failed\n");
}
```
the reason it can do this is the new operator is marked as throwing an
exception on failure, which means the error path is unreachable. As we
don't have C++ exceptions in ArduPilot could (and do!) have code that
ends up losing protection against allocation failures
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