document -Dswift_std in release notes

bonzini · jpakkane · commit 76323ad829e5 · 2025-04-20T16:26:02.000+03:00
diff --git a/docs/markdown/snippets/swift-std.md b/docs/markdown/snippets/swift-std.md
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+## New `swift_std` compiler option
+
+A new compiler option allows to set the language version that is passed
+to swiftc (`none`, `4`, `4.2`, `5` or `6`).
