x86-64: Add vector cbrt/cbrtf to libmvec microbenchmark

x86-64: Add vector cbrt/cbrtf to libmvec microbenchmark

Add vector cbrt/cbrtf and input files to libmvec microbenchmark.

libmvec-cbrt-inputs:
  90% Normal random distribution
  range: (-DBL_MAX, DBL_MAX)
  mean: 0.0
  sigma: 10.0
  10% uniform random distribution in range (-1000.0, 1000.0)

libmvec-cbrtf-inputs:
  90% Normal random distribution
  range: (-FLT_MAX, FLT_MAX)
  mean: 0.0f
  sigma: 10.0f
  10% uniform random distribution in range (-1000.0f, 1000.0f)

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>