svdvals is alarmingly slow

@simonbyrne I had a chance to try it, and the results are not good:

julia> @btime svdvals($B);
  1.371 ms (11 allocations: 138.20 KiB)

julia> versioninfo()
Julia Version 0.6.2
Commit d386e40c17* (2017-12-13 18:08 UTC)
Platform Info:
  OS: Windows (x86_64-w64-mingw32)
  CPU: Intel(R) Core(TM) i7-7820HQ CPU @ 2.90GHz
  WORD_SIZE: 64
  BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY Prescott)
  LAPACK: libopenblas64_
  LIBM: libopenlibm
  LLVM: libLLVM-3.9.1 (ORCJIT, broadwell)

This is the same machine where Julia on a Linux VirtualBox takes 673us.

One more thing, on Linux I build Julia from source, while on Windows I’m using the precompiled binary. I don’t expect this to cause much difference (but you never know).