[LifetimeSafety] Support C compound literals

LifetimeSafety does not fully model C compound literals yet.

Minimal repro:

```c
int *bad(void) {
int *p = &(int){12};
return p; // should warn
}
```

https://godbolt.org/z/6oPvfr9bn

In C, compound literal has automatic storage duration, so this should behave roughly like returning the address of an unnamed local variable.

Expected: warn that the returned pointer refers to storage that does not live long enough.

This should remain OK however:

```c
int ok(void) {
int *p = &(int){12};
*p = 100;
return *p;
}
```