Rename "ADDO" to "SADDO" and "UADDO". The "UADDO" isn't equivalent to "ADDC"

Rename "ADDO" to "SADDO" and "UADDO". The "UADDO" isn't equivalent to "ADDC"
because the boolean it returns to indicate an overflow may not be treated like
as a flag. It could be stored to memory, for instance.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@59780 91177308-0d34-0410-b5e6-96231b3b80d8