[Issue 24447] ImportC: extern symbols cannot have initializers

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24447

--- Comment #1 from dave287091 at gmail.com ---
`extern int x = 3;` at file scope should be treated the same as `int x = 3;`.

Section 6.9.2 defines the rules and has an example.

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