[clang] [flang] [flang][driver] Avoid mentions of Clang in Flang's command line reference. (PR #88932)

[David Spickett via cfe-commits]

DavidSpickett wrote:

> Clang is also mentioned for the diagnostic warnings reference, which mostly applies to C/C++/Obj-C, not Fortran. https://github.com/llvm/llvm-project/pull/81726 already tried to fix this, and I don't know a better solution.

Do you mean that this PR fixes this, or that you noticed this problem while working on this?

If it's the latter it may be as @banach-space mentioned to me, that the `docbrief` is still shared between Flang and Clang. This could be solved in a similar, albeit tedious way to what I did for the help text.

https://github.com/llvm/llvm-project/pull/88932