This used to be necessary for a correct linker order, but ever since the
introduction of symbols.o adding the symbols in question to symbols.o
would work just as well. We do still add dependencies on the panic runtime
to the local crate, but not for #![needs_panic_runtime] crates.
This also removes the runtime-depends-on-needs-runtime test.
inject_dependency_if used to emit this error, but with symbols.o it is
no longer important that there is no dependency and in fact it may be
nice to have panic_abort and panic_unwind directly depend on libstd in
the future for calling std::process::abort().
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