[flang][mlir] Fix-forward heap use-after-free in #155348 (#164712)

`mapInfoOp.getMembers()` on line 258 is use-after-free, because
cloneModifyAndErase (line 255) erased `mapInfoOp`. Fix the issue by
replacing subsequent `mapInfoOp` usages with `clonedOp`.

Similarly, update `memberMapInfoOp` to avoid subsequent use-after-free.

Author: thurstond

mlir/lib/Dialect/OpenMP/Transforms/OpenMPOffloadPrivatizationPrepare.cpp

@@ -252,14 +252,17 @@ class PrepareForOMPOffloadPrivatizationPass
         // variable, rewrite all the uses of the original variable with
         // the heap-allocated variable.
         rewriter.setInsertionPoint(targetOp);
-        rewriter.setInsertionPoint(cloneModifyAndErase(mapInfoOp));
+        mapInfoOp = cast<omp::MapInfoOp>(cloneModifyAndErase(mapInfoOp));
+        rewriter.setInsertionPoint(mapInfoOp);
 
         // Fix any members that may use varPtr to now use heapMem
         for (auto member : mapInfoOp.getMembers()) {
           auto memberMapInfoOp = cast<omp::MapInfoOp>(member.getDefiningOp());
           if (!usesVarPtr(memberMapInfoOp))
             continue;
-          rewriter.setInsertionPoint(cloneModifyAndErase(memberMapInfoOp));
+          memberMapInfoOp =
+              cast<omp::MapInfoOp>(cloneModifyAndErase(memberMapInfoOp));
+          rewriter.setInsertionPoint(memberMapInfoOp);
 
           if (memberMapInfoOp.getVarPtrPtr()) {
             Operation *varPtrPtrdefOp =