Override assert handler

[kinke]

On Saturday, 17 August 2024 at 09:31:53 UTC, Manu wrote:
> I mean, there's also the `assertHandler()` stuff, but I don't 
> really see the point; I'd rather just replace the assert 
> handler symbol directly. Using `assertHandler` is awkward 
> because you need a static constructor to register it at 
> runtime, and then anything you do in your assert handler almost 
> inevitably leads to bootup issues with cyclic module 
> dependencies because everything leads back to assert.

You can set the handler in a CRT constructor, which avoids any 
cycles and makes sure it is installed before initializing 
druntime (`rt_init()`), so should really cover all asserts:
```
pragma(crt_constructor)
void setupAssertHandler()
{
     import core.exception : assertHandler;
     assertHandler = &myAssertHandler;
}

void myAssertHandler(string file, size_t line, string msg) nothrow
{
     // print...
     import core.stdc.stdlib;
     abort(); // or something like that
}
```

`@core.attribute.weak` isn't implemented by DMD, plus needs 
emulation on Windows (done by LDC) with according limitations. 
The extra indirection via that custom assert handler in druntime 
works e.g. for a pre-linked druntime DLL too.