[llvm] [Github] Enable warnings as errors on flang sphinx build (PR #72723)

[Kiran Chandramohan via llvm-commits]

kiranchandramohan wrote:

> We'll probably need to wait a little bit before merging this, but there's only one final warning that I can see before this is ready to merge:
> 
> ```
> /tmp/llvm-project/build/tools/flang/docs/Source/FlangCommandLineReference.rst:176: WARNING: unknown document: 'DiagnosticsReference'
> ```
> 
> Once that gets fixed, we should be able to get this in.

This warning is coming from the fact there is a reference to this document in Options.td (https://github.com/llvm/llvm-project/blob/37fa32785e23198fc9585296e990b18abfd2ba90/clang/include/clang/Driver/Options.td#L133). Options.td is shared between flang and clang. While generating documentation for Flang this reference is present and that causes the warning. We do not generate DiagnosticsReference at the moment in Flang and do not have a plan for this at the moment. The code for Diagnostics sits inside Clang Basic directories, while in Flang it is in the Semantics code.

I will need help to fix this issue.

https://github.com/llvm/llvm-project/pull/72723