We end up needing to do this in any driver subcommand that reaches into
external code that may not be fully fuzz-clean. No need to grow multiple
different diagnostics for each, we can use a common diagnostic.
This initializes the DriverResult::per_file_success field explicitly
with `= {}` in order to encode that DriverResult can be constucted via
aggregate initialization while omitting the per_file_success field. This
prevents -Wmissing-designated-field-initializers from firing in newer
clang versions when constructing DriverResult like:
```
return {.success = false};
```
Newer clang-tidy warns that the `= {}` is redundant however it is not,
as its marking which fields need to be explicitly initialized. So we
suppress it.
Note the purpose here is to make it simpler to add more subcommands,
without adding a lot of things to Driver.
This creates a copy of CodegenOptions, but it was double-registered at
present which felt odd. It's also fairly small right now. If this
becomes an issue, maybe we can look into using optional for delayed
initialization, or just go back to straight sharing.
---------
Co-authored-by: josh11b <15258583+josh11b@users.noreply.github.com>