Missing optimization with multiply-inlined magic statics

If a function with magic static is inlined into another function multiple times, it is inlined very literally; code for checking that the static variable was initialized, initializing it if it wasn't, and even the load itself are duplicated.

[*Example on godbolt*](https://godbolt.org/z/xsYT8nMd6)
```cpp
int opaque();
int adjust() {
static int base = opaque(); // force non-constant initialization
return base;
}

int double_adjusted() {
return adjust() + adjust();
}
```

The code for `double_adjusted` should check the guard variable just once, and produce the return value with the equivalent of `2 * adjust()`.