Make the ccache-free case look like the ccache case.

This fixes a problem with `make check` clang -Werror failing due to an
unused -Llib arg.
auto merge of #10771 : pnkfelix/rust/fix-make-check-for-ccacheless-clang, r=acrichto

 This fixes a problem with `make check` clang -Werror failing due to an unused -Llib arg.