[Issue 20012] export inside mixin doesn't seem to work

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20012

--- Comment #7 from Manu <turkeyman at gmail.com> ---
It's just one declaration among a bunch of other stuff that is inserted into
the global scope, and it's the only declaration that doesn't 'work'. It
shouldn't be separated from all its associated declarations, and it's super
weird that that's required.

Mixin templates into the global scope appear in every single reflection-driven
application I've ever written. One part of that generated code is the
entrypoint function which registers the modules contents with the module
loader.

Seriously, just fix this. It's a bug.

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