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.