Log Message:
fftw: updated to 3.3.8

FFTW 3.3.8:

* Fixed AVX, AVX2 for gcc-8.

  By default, FFTW 3.3.7 was broken with gcc-8.  AVX and AVX2 code
  assumed that the compiler honors the distinction between +0 and -0,
  but gcc-8 -ffast-math does not.  The default CFLAGS included -ffast-math.
  This release ensures that FFTW works with gcc-8 -ffast-math, and
  removes -ffast-math from the default CFLAGS for good measure.