Log Message:
fftw*: update to 3.3.9

FFTW 3.3.9:

* New API fftw_planner_nthreads() returns the number of threads
  currently being used by the planner.

* Fix incorrect math in 128-bit generic SIMD

* Fix wisdom for avx512.

  The avx512 alignment requirement was set to 64 bytes, but this is
  wrong.  Alignment requirements are a property of the platform (e.g.,
  x86) and not of the instruction set (e.g., AVX).  Among other
  things, this broke wisdom with avx512.

  Note that avx512 support is still experimental because the FFTW
  authors have no avx512 hardware available for testing.

* fftw_threads_set_callback function to change the threading backend at runtime.