[Attributor] Fix an issue that could potentially cause AccessList and OffsetBins out of sync

The implementation of `AAPointerInfo::RangeList::set_difference` doesn't
consider the case where two ranges have the same offset but different sizes.
This could causes `AccessList` and `OffsetBins` out of sync because a range has
been already updated in `AccessList` but missing in `ToRemove`.

I do have a reproducer but the reproducer itself is 248kb. `llvm-reduce` can't
further reduce it. Not sure how I can make a smaller reproducer.

Fix SWDEV-479757.

Author: shiltian

llvm/include/llvm/Transforms/IPO/Attributor.h

@@ -5818,7 +5818,10 @@ struct AAPointerInfo : public AbstractAttribute {
     static void set_difference(const RangeList &L, const RangeList &R,
                                RangeList &D) {
       std::set_difference(L.begin(), L.end(), R.begin(), R.end(),
-                          std::back_inserter(D), RangeTy::OffsetLessThan);
+                          std::back_inserter(D),
+                          [](const RangeTy &L, const RangeTy &R) {
+                            return (L.Offset < R.Offset) || (L != R);
+                          });
     }
 
     unsigned size() const { return Ranges.size(); }