[flang] Carry over the derived type from MOLD

[clementval]

Summary

Derived type from the MOLD was not carried over
to the newly allocated pointer or allocatable.
This may lead to wrong dynamic type when the pointer or allocatable
is polymorphic as shown in the example below:

type :: p1
  integer :: a
end type

type, extends(p1) :: p2
  integer :: b
end type

class(p1), pointer :: p(:)

allocate(p(5), MOLD=p2(1,2))

flang/runtime/allocatable.cpp

void RTNAME(AllocatableApplyMold)(
   if (descriptor.IsAllocated()) {
     // 9.7.1.3 Return so the error can be emitted by AllocatableAllocate.
     return;
   }
   descriptor = mold;
   descriptor.set_base_addr(nullptr);
   descriptor.raw().attribute = CFI_attribute_allocatable;
   descriptor.raw().rank = rank;
+  if (auto *descAddendum{descriptor.Addendum()}) {
+    if (const auto *moldAddendum{mold.Addendum()}) {
+      if (const auto *derived{moldAddendum->derivedType()}) {
+        descAddendum->set_derivedType(derived);
+      }
+    }
+  }
 }
 
 int RTNAME(AllocatableAllocate)(Descriptor &descriptor, bool hasStat,
     const Descriptor *errMsg, const char *sourceFile, int sourceLine) {
   Terminator terminator{sourceFile, sourceLine};
   if (!descriptor.IsAllocatable()) {
     return ReturnError(terminator, StatInvalidDescriptor, errMsg, hasStat);
   }

flang/runtime/pointer.cpp

 }
 
 void RTNAME(PointerApplyMold)(
     Descriptor &pointer, const Descriptor &mold, int rank) {
   pointer = mold;
   pointer.set_base_addr(nullptr);
   pointer.raw().attribute = CFI_attribute_pointer;
   pointer.raw().rank = rank;
+  if (auto *pointerAddendum{pointer.Addendum()}) {
+    if (const auto *moldAddendum{mold.Addendum()}) {
+      if (const auto *derived{moldAddendum->derivedType()}) {
+        pointerAddendum->set_derivedType(derived);
+      }
+    }
+  }
 }
 
 void RTNAME(PointerAssociateScalar)(Descriptor &pointer, void *target) {
   pointer.set_base_addr(target);
 }
 
 void RTNAME(PointerAssociate)(Descriptor &pointer, const Descriptor &target) {
   pointer = target;