[Issue 24513] `pure` can be used as `auto`

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24513

--- Comment #2 from basile-z <b2.temp at gmx.com> ---
that's completly stupid. Nobody would accept that in phobos. Just imagine my
friend, someone who makes a PR that is like

```
pure takeWhile(T)(auto ref T t);
```

any human being would open a review comment to say

"why the heck dont you use auto"

and then you have the complete ashole who comes and say

> An auto function is declared without a return type. Auto functions can use any valid StorageClass, not just auto

that's absurd.

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