[clang] [flang] [flang][Driver] Better error message when multiple actions are specified (PR #165575)

[David Spickett via cfe-commits]

https://github.com/DavidSpickett commented:

I forgot all about this issue, thanks for working on it. The new error format would certainly have solved my original problem.

https://github.com/llvm/llvm-project/pull/165575