(a) Slight rethink on i64 zero/sign/any extend code - use a shuffle to
directly zero-extend i32 to i64, but use rotates and shifts for
sign extension. Also ensure unified register consistency.
(b) Add new test harness for i64 operations: i64ops.ll
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@59970 91177308-0d34-0410-b5e6-96231b3b80d8
