[flang] [llvm] [flang] implement show_descriptor intrinsic, a non-standard extension (PR #169137)

[Valery Dmitriev via llvm-commits]

valerydmit wrote:

Output example:
```
Descriptor @ 0x7ffcec05b7e8:
  base_addr 0x555f2bf9e070
  elem_len  4
  version   20240719
  scalar
  type      27 "REAL(kind=4)"
  attribute 0
  extra     0
    addendum  0
    alloc_idx 0
Descriptor @ 0x7ffcec05b7b8:
  base_addr 0x555f2bf9e074
  elem_len  4
  version   20240719
  rank      1
  type      27 "REAL(kind=4)"
  attribute 0
  extra     0
    addendum  0
    alloc_idx 0
  dim[0] lower_bound 1
         extent      3
         sm          4
```

https://github.com/llvm/llvm-project/pull/169137