Rollup merge of #138751 - Jeff-A-Martin:used-with-archive-test-fuchsia, r=jieyouxu

Fix the "used_with_archive" test on Fuchsia

This change adds Fuchsia OS as a target to the cfg_attr in the pre_main_constructor external declaration. This allows the "tests/ui/attributes/used_with_archive.rs" to pass against Fuchsia.

Author: matthiaskrgr