[OpenMP][MLIR] Fix llvm::sort comparator.

The current comparator doesn't work correctly when two identical entries with -1 are compared. The comparator returns `first` is case when `aIndex == -1 && bIndex == -1`, but it should continue as those indexes are the same.

Author: olegshyshkov

mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp

@@ -2155,18 +2155,14 @@ getFirstOrLastMappedMemberPtr(mlir::omp::MapInfoOp mapInfo, bool first) {
           int aIndex = indexValues[a * shape[1] + i];
           int bIndex = indexValues[b * shape[1] + i];
 
+          if (aIndex == bIndex) continue;
+
           if (aIndex != -1 && bIndex == -1)
             return false;
 
           if (aIndex == -1 && bIndex != -1)
             return true;
 
-          if (aIndex == -1)
-            return first;
-
-          if (bIndex == -1)
-            return !first;
-
           // A is earlier in the record type layout than B
           if (aIndex < bIndex)
             return first;