Auto merge of #101792 - lqd:rust-lld, r=petrochenkov

Only specify `--target` by default for `-Zgcc-ld=lld` on wasm

On macOS, it's not yet clear which cases of clang/OS/target/SDK version impact how to find ld/lld/rust-lld. The `--target` argument is not needed on our current targets with a vanilla config to do so, but may be in some cases ?

That is, things look to be different and more subtle than suggested in rust-lang/rust#97402 (comment).

Specifying this argument unconditionally currently breaks `-Zgcc-ld=lld` on the 10.7+ targets on x64 macOS. Vanilla configs on x64 and aarch64 don't seem to need it to be able to find `rust-lld`.

This fixes #101653 on macOS (I've tried on x64 and aarch64: vanilla installs with the most recent command line tools available for each of the OS versions I have access to, `run-make/issue-71519` passes).

I didn't expect the previous PRs to fail because of the existing tests, but CI does not actually run those tests yet, which explains the regressions. I was hoping to fix those in this PR but it's more involved (building lld is required for the tests to run, llvm/lld is not built on the test builders but on the dist builders, the dist builders don't run tests). This PR is just to unblock current users on macOS who have reported issues, but a regression could happen in the future by mistake until then.

r? `@petrochenkov`

Author: bors