Auto merge of #136098 - jyn514:linker-output, r=saethlin

Downgrade `linker-warnings` to allow-by-default

This needs more time to bake before we turn it on. Turning it on early risks people silencing the warning indefinitely, before we have the chance to make it less noisy.

cc rust-lang/rust#136096
fixes rust-lang/rust#136086 (comment)

r? `@saethlin` cc `@Noratrieb` `@bjorn3`

`@rustbot` label A-linkage L-linker_messages

Author: bors