[clang] [flang] [flang/clang] Adding use of Clang's diagnostics in Flang (PR #130593)

[Kiran Chandramohan via cfe-commits]

kiranchandramohan wrote:

Thanks @JDPailleux for the patch. I have not gone into the patch in detail but would like to provide some context.

In general, we aim to only depend on libClangDriver and move it to LLVM so that Flang need not depend on Clang or its libraries. If this patch increases the dependency on Clang it might not be acceptable.

https://github.com/llvm/llvm-project/pull/130593