If a test would still fail post-autoupdate due to either mismatched
`fail_` prefix or due to being NOAUTOUPDATE, the test is reported as `?`
instead of `.` in the incremental progress output, and a message is
listed after the progress output describing the problem. For example:
```console
Problems that require manual fixes:
- `toolchain/check/testdata/basics/zz_prefix_probe.carbon` split `bad_missing_prefix.carbon` failed; if failure is expected, add the `fail_` prefix.
- `toolchain/driver/testdata/fail_config.carbon` succeeded; if success is expected, remove the `fail_` prefix.
```
This change caused the `NOAUTOUPDATE` test
`toolchain/driver/testdata/fail_config.carbon` to fail, because when run
under autoupdate (or with `bazel run`), the install manifest would be
present, and the test is checking that it's not. Fixed by using the VFS
to look for the manifest, which then required fixing
toolchain/driver:driver_test to set up a real filesystem VFS so that it
*could* find the manifest.
With this change, there should no longer be a reason to manually run
file_test in addition to running autoupdate.
Assisted-by: Claude via Antigravity
Richard Smith
d9106700c6