Fix Issue 18474 - Postblit not working in shared structs

[RazvanN7]

No description provided.

[dlang-bot]

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	18474	normal	Postblit not working in shared structs

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub fetch digger
dub run digger -- build "master + dmd#8098"

[andralex]

thx! cc @WalterBright