[test] Driver/ftime-trace.cpp: work around -Wmsvc-not-found

There may be one extra warning. Just make the check less strict.
```
clang: warning: unable to find a Visual Studio installation; try running Clang from a developer command prompt [-Wmsvc-not-found]
clang: warning: argument unused during compilation: '-ftime-trace' [-Wunused-command-line-argument]
clang: warning: argument unused during compilation: '-ftime-trace=e' [-Wunused-command-line-argument]
clang: warning: argument unused during compilation: '-ftime-trace-granularity=1' [-Wunused-command-line-argument]
```