On Borrow Checking

[Richard (Rikki) Andrew Cattermole]

Further proof that clang can do more than what DIP1000 can:

``$clang --analyze``

```c++
void assign(int* input [[clang::lifetime_capture_by(output)]], int** 
output) {
     *output = input;
}

int* global;

void grab() {
     int var;
     assign(&var, &global);
}
```

Output:

```
<source>:9:5: warning: Address of stack memory associated with local 
variable 'var' is still referred to by the global variable 'global' upon 
returning to the caller.  This will be a dangling reference 
[core.StackAddressEscape]
     8 |     int var;
       |     ~~~~~~~
     9 |     assign(&var, &global);
       |     ^~~~~~~~~~~~~~~~~~~~~
1 warning generated.
```

https://godbolt.org/z/nY518WqTr