mk: Use host llvm linkage paths, not target ones

We only build LLVM for the host architecture, not the target architecture, so
this was just a minor typo in the parameters uses.

Closes #19383
Fix typo in tests makefile
auto merge of #19425 : frewsxcv/rust/patch-1, r=steveklabnik

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auto merge of #19417 : alexcrichton/rust/issue-19383, r=huonw

We only build LLVM for the host architecture, not the target architecture, so
this was just a minor typo in the parameters uses.

Closes #19383