Don't force the build of toos/lto as a static lib.

Any uses of tools/lto as a static lib should probably move to lib/LTO.
This was also never implemented in the configure build, so this reduces
the differences among the two.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211852 91177308-0d34-0410-b5e6-96231b3b80d8