Model calls as *both* using *and* killing O0..O5, because callees use the

Model calls as *both* using *and* killing O0..O5, because callees use the
argument values passed in (so they're not dead until *after* the call),
and callees are free to modify those registers.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16882 91177308-0d34-0410-b5e6-96231b3b80d8