regression: malformed link attribute input (accepted breakage; might need more downstream patches)

[BoxyUwU]

• https://crater-reports.s3.amazonaws.com/beta-1.91-2/beta-2025-09-21/reg/sandbox-ipc-0.4.0/log.txt
• https://crater-reports.s3.amazonaws.com/beta-rustdoc-1.91-2/beta-2025-09-21/gh/TheOnlyMrCat.lok-r4/log.txt
• https://crater-reports.s3.amazonaws.com/beta-rustdoc-1.91-2/beta-2025-09-21/reg/sandbox-ipc-0.4.0/log.txt

[INFO] [stdout] error[E0539]: malformed `link` attribute input
[INFO] [stdout]    --> src/unix/sharedmem.rs:188:1
[INFO] [stdout]     |
[INFO] [stdout] 188 | #[link = "c"]
[INFO] [stdout]     | ^^^^^^^^^^^^^ expected this to be a list
[INFO] [stdout]     |
[INFO] [stdout]     = note: for more information, visit <https://doc.rust-lang.org/reference/items/external-blocks.html#the-link-attribute>
[INFO] [stdout] help: try changing it to one of the following valid forms of the attribute

this is excluding the hundreds of link = "dl" regressions that were filed separately

[fmease]

Lang-FCP'ed in #143193.

[fmease]

Might need more downstream patches or issues; CC @JonathanBrouwer @jdonszelmann

If everything has been covered already, then just close this issue as "not planned" :)