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

[Valery Dmitriev via llvm-commits]

valerydmit wrote:

> I reverted this because of the ongoing buildbot break. It already interfered with diagnosing #170142

Thanks for reverting this for me. I had a busy morning today so could not react quickly enough.

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