[Build] Errors in fscomp.txt are not printed to the log

Make FSComp.txt fail: just add something invalid, like ``xxxxxxxxxxxxx`` to the end

#### Actual:

```
1>------ Build started: Project: FSharp.Compiler.Private, Configuration: Debug Any CPU ------
1>Done building project "FSharp.Compiler.Private.fsproj" -- FAILED.
1>
1>Build FAILED.
========== Build: 0 succeeded, 1 failed, 1 up-to-date, 0 skipped ==========
```

#### Expected: any indication that there is an issue with FSComp. Even just printing a generic error "FScomp failed" would be better than nothing.