[Issue 20307] New: Difference for `deprecated alias a = b` vs. `deprecated alias b a`

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20307

          Issue ID: 20307
           Summary: Difference for `deprecated alias a = b` vs.
                    `deprecated alias b a`
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: kinke at gmx.net

Compile this with `-w` (https://run.dlang.io/is/B5ifPu):

```
deprecated ("bla") void foo();

deprecated alias foo f;         // 2 deprecation msges
deprecated alias g = foo;       // no deprecation msg
deprecated ("bla") alias foo h; // no deprecation msg either
```

Output:
```
onlineapp.d(3): Deprecation: function `onlineapp.foo` is deprecated - bla
onlineapp.d(3): Deprecation: function `onlineapp.foo` is deprecated - bla
```

This is actually adapted from druntime (core.sys.windows.odbcinst).

1) Why is there a difference between `deprecated alias foo f` and `deprecated
alias f = foo`?
2) Why does adding a msg make a difference?
3) Why is the deprecation msg printed twice for the same trivial alias
declaration?

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