rustc_target: Update some old naming around self contained linking

[petrochenkov]

The "fallback" naming pre-dates introduction of -Clink-self-contained. Noticed when reviewing https://github.com/rust-lang/rust/pull/99500.

This PR doesn't break any json target spec, but supporting per-linker-flavor startup objects needed by https://github.com/rust-lang/rust/pull/99500 will break them, so maybe next time I'll remove the compatibility names.

[rust-highfive]

r? @lcnr

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[rust-highfive]

:warning: Warning :warning:

• These commits modify compiler targets. (See the Target Tier Policy.)

[luqmana]

+1 This naming makes the option a lot less confusing. LGTM

[lcnr]

r? compiler

[fee1-dead]

r? compiler

[davidtwco]

@bors r+

[bors]

:pushpin: Commit e74299b6f10d525ec64d8b6e5c0587624d256b2b has been approved by davidtwco

It is now in the queue for this repository.

[bors]

:umbrella: The latest upstream changes (presumably #100426) made this pull request unmergeable. Please resolve the merge conflicts.

[petrochenkov]

@bors r=davidtwco

[bors]

:pushpin: Commit 8fa707ab417b7c6b2cc9a57435cbc48b53c69f7e has been approved by davidtwco

It is now in the queue for this repository.