This runtime API can be used to lower any flavor of array constructors,
but is mainly intended to be used with:
- array constructors for which the extent or length parameters cannot
be computed without lowering some ac-value or ac-implied-do-control
that cannot be pre-evaluated.
- array constructors of a derived type with allocatable component where
copy is not trivial or PDTS.
Example of use cases:
- `[((i+j,i=1, ifoo()), j=1,n)]` where ifoo() is not pure.
- `[return_allocatable_array(), return_allocatable_array()]`
Differential Revision: https://reviews.llvm.org/D144411
