[lld] Use -o /dev/null in test when output is not needed.
Feedback nit from rL364998
I'm not sure this is correct.
The output file %t.archive.o appears to be used below on line 6, so outputting to /dev/null here causes the test to fail, I think.
As far as I can tell the review comments for https://reviews.llvm.org/D63781 refer to the -o out.wasm on this line.
This is correct, but I would no bother updating this single case. I had a change to update most cases luke this, I was just not sure if I should update them all in batch.