[flang] [llvm] [flang/flang-rt] Implement show_descriptor intrinsic, a non-standard extension. (PR #170389)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `ppc64le-flang-rhel-clang` running on `ppc64le-flang-rhel-test` while building `flang-rt,flang` at step 6 "test-build-unified-tree-check-flang".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/157/builds/42742

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-flang) failure: test (failure)
******************** TEST 'Flang :: Semantics/bug159554.f90' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
"/home/buildbots/llvm-external-buildbots/workers/env/bin/python3.8" /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/llvm-project/flang/test/Semantics/test_errors.py /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/llvm-project/flang/test/Semantics/bug159554.f90 /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/build/bin/flang -fc1
# executed command: /home/buildbots/llvm-external-buildbots/workers/env/bin/python3.8 /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/llvm-project/flang/test/Semantics/test_errors.py /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/llvm-project/flang/test/Semantics/bug159554.f90 /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/build/bin/flang -fc1
# .---command stdout------------
# | --- 
# | +++ 
# | @@ -1 +0,0 @@
# | 
# | actual at 3: 'c_funloc' should not be the name of both a generic interface and a procedure unless it is a specific procedure of the generic [-Whomonymous-specific]
# | 
# | FAIL
# `-----------------------------
# error: command failed with exit status: 1

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/170389