Add support for non-allocatable module-level CUDA managed variables
using pointer indirection through a companion global in
__nv_managed_data__. The CUDA runtime populates this pointer with the
unified memory address via __cudaRegisterManagedVar and
__cudaInitModule.
1. Create a .managed.ptr companion global in the __nv_managed_data__
section and register it with _FortranACUFRegisterManagedVariable
(CUFAddConstructor.cpp)
2. Call __cudaInitModule after registration to populate the managed
pointer (registration.cpp)
3. Annotate managed globals in gpu.module with nvvm.managed for PTX
.attribute(.managed) generation (cuda-code-gen.mlir)
4. Suppress cuf.data_transfer for assignments to/from non-allocatable
module managed variables, since cudaMemcpy would target the shadow
address rather than the actual unified memory (tools.h)
5. Preserve cuf.data_transfer for device_var = managed_var assignments
where explicit transfer is still required
c4e6cf0abf