[LTO] Add a test to ensure we reject negative opt level.
[LTO] Add a test to ensure we reject negative opt level.

We already got this right, but it never hurts adding another
test, in case we'll change the handling in the future, to ensure
we don't break it.


git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@265256 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld