Add a new getMergeValues method that does not need

Add a new getMergeValues method that does not need
to be passed the list of value types, and use this
where appropriate.  Inappropriate places are where
the value type list is already known and may be
long, in which case the existing method is more
efficient.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53035 91177308-0d34-0410-b5e6-96231b3b80d8