This is really old. C++, Java are mature languages. Scala hit 2.11 in March 2014, while Go version 1 was released in March 2012 and currently is at 1.3. Versions don't tell the whole story, but they do matter.
The benchmarking itself was done in a simple and
fairly un-scientific fashion.
... older Pentium IV workstation. Run-times were
measured using wall-clock time.
but still a good read about tweaking c++ (I think at the time, clang and gcc were still implementing the C++11 standard features).
http://blog.golang.org/profiling-go-programs