Tweak wasm_base target spec to indicate linker is not GNU and update linker inferring logic for wasm-ld.

[luqmana]

Reported via Zulip: we try passing --as-needed to the linker if it's GNU ld which wasm-ld is not. Usually this isn't an issue for wasm as we would use the WasmLd linker driver but because the linker in question (wasm32-unknown-wasi-wasm-ld) ended with -ld our linker inferring logic used the GccLinker implementations. (UPD: The linker inferring logic actually didn't apply in this case because the linker is actually invoked through gcc in the reported issue. But it's still worth updating the logic I think.)

This change then has 2 parts:

1. Update wasm_base target spec to indicate linker_is_gnu: false plus a few additions of target.is_like_wasm to handle flags wasm-ld does in fact support.
2. Improve the linker detection logic to properly determine the correct flavor of wasm linker we're using when we can.

We need to add the new target.is_like_wasm branches to handle the case where the "linker" used could be something like clang which would then under the hood call wasm-ld.

[rust-highfive]

r? @petrochenkov

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[petrochenkov]

@bors r+

[bors]

📌 Commit f667aca has been approved by petrochenkov