I wonder -- "-fuse-ld" has some somewhat surprising behavior in how clang ends up discovering the linker. I think that even if clang has a sibling `lld` in the same distribution, "-fuse-ld=lld" will pick "ld.lld" from the $PATH if it's present in there before the directory where clang and lld are installed.
So maybe that "--ld-path" option helps resolve ambiguity by expecting an explicit path instead of a linker name.
or persitant in your project:
.cargo/config.toml
[target.x86_64-unknown-linux-gnu] linker = "clang" rustflags = ["-C", "link-arg=-fuse-ld=/PATH/TO/mold"]