[Issue 23030] importC: errors using typedef struct after first use as const

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23030

duser at neet.fi changed:

           What    |Removed                     |Added
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           Severity|normal                      |major

--- Comment #3 from duser at neet.fi ---
increasing the importance since this would become a regression in v2.100.0
compared to v2.099.1

if there's no immediate fix available, then i'd prefer if the PR that caused
this was reverted since the bug(s) it fixes weren't that common compared to
this one

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