ENH: Update FFTW to latest release
ENH: Update FFTW to latest release

Update from 3.3.4 (circa 2014) to 3.3.8 (circa 2018)
to include performance updates and improved compiler
compatibility.

FFTW 3.3.8 May 28th, 2018
  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.
FFTW 3.3.7 Oct 29th, 2017
  Experimental support for CMake
  The primary build mechanism for FFTW remains GNU autoconf/automake.
  CMake support is meant to offer an easy way to compile FFTW on
  Windows, and as such it does not cover all the features of the
  automake build system, such as exotic cycle counters, cross-compiling,
  or build of binaries for a mixture of ISA's (e.g., amd64 vs amd64+avx
    vs amd64+avx2). Patches are welcome.

  Fixes for armv7a cycle counter.
  Official support for aarch64, now that we have hardware to test it.
  Tweak usage of FMA instructions in a way that favors newer processors (Skylake and Ryzen) over older processors (Haswell).
  tests/bench: use 64-bit precision to compute mflops.
FFTW 3.3.6-pl2 Mar 25th, 2017
  Bugfix: MPI Fortran-03 headers were missing in FFTW 3.3.6-pl1.
FFTW 3.3.6-pl1 (withdrawn) Jan 16th, 2017
  Bugfix: FFTW 3.3.6 had the wrong libtool version number, and generated shared libraries of the form libfftw3.so.2.6.6 instead of libfftw3.so.3.*.
FFTW 3.3.6 (withdrawn) Jan 15th, 2017
  The fftw_make_planner_thread_safe() API introduced in 3.3.5 didn't work, and this 3.3.6 fixes it. Sorry about that.
  Compilation fixes for IBM XLC.
  Compilation fixes for threads on Windows.
  fix SIMD autodetection on amd64 when (_MSC_VER > 1500)
FFTW 3.3.5 Jul 31, 2016
  New SIMD support:
  Power8 VSX instructions in single and double precision. To use, add --enable-vsx to configure.
  Support for AVX2 (256-bit FMA instructions). To use, add --enable-avx2 to configure.
  Experimental support for AVX512 and KCVI. (--enable-avx512, --enable-kcvi) This code is expected to work but the FFTW maintainers do not have hardware to test it.
  Support for AVX128/FMA (for some AMD machines) (--enable-avx128-fma)
  Double precision Neon SIMD for aarch64. This code is expected to work but the FFTW maintainers do not have hardware to test it.
  generic SIMD support using gcc vector intrinsics.
  Add fftw_make_planner_thread_safe() API.
  fix #18 (disable float128 for CUDACC).
  fix #19: missing Fortran interface for fftwq_alloc_real.
  fix #21 (don't use float128 on Portland compilers, which pretend to be gcc).
  fix: Avoid segfaults due to double free in MPI transpose.
  Special note for distribution maintainers: Although FFTW supports a
  zillion SIMD instruction sets, enabling them all at the same time is a
  bad idea, because it increases the planning time for minimal gain. We
  recommend that general-purpose x86 distributions only enable SSE2 and
  perhaps AVX. Users who care about the last ounce of performance should
  recompile FFTW themselves.

Kitware/ITK,LucasGandel/ITK,Kitware/ITK,hjmjohnson/ITK,BRAINSia/ITK,richardbeare/ITK,vfonov/ITK,thewtex/ITK,Kitware/ITK,thewtex/ITK,thewtex/ITK,Kitware/ITK,malaterre/ITK,richardbeare/ITK,richardbeare/ITK,malaterre/ITK,thewtex/ITK,richardbeare/ITK,hjmjohnson/ITK,BRAINSia/ITK,vfonov/ITK,InsightSoftwareConsortium/ITK,vfonov/ITK,malaterre/ITK,malaterre/ITK,thewtex/ITK,LucasGandel/ITK,hjmjohnson/ITK,InsightSoftwareConsortium/ITK,InsightSoftwareConsortium/ITK,BRAINSia/ITK,InsightSoftwareConsortium/ITK,vfonov/ITK,thewtex/ITK,LucasGandel/ITK,hjmjohnson/ITK,vfonov/ITK,vfonov/ITK,malaterre/ITK,vfonov/ITK,vfonov/ITK,Kitware/ITK,BRAINSia/ITK,malaterre/ITK,BRAINSia/ITK,BRAINSia/ITK,InsightSoftwareConsortium/ITK,malaterre/ITK,BRAINSia/ITK,LucasGandel/ITK,thewtex/ITK,hjmjohnson/ITK,richardbeare/ITK,hjmjohnson/ITK,Kitware/ITK,LucasGandel/ITK,InsightSoftwareConsortium/ITK,LucasGandel/ITK,malaterre/ITK,richardbeare/ITK,LucasGandel/ITK,hjmjohnson/ITK,Kitware/ITK,InsightSoftwareConsortium/ITK,vfonov/ITK,LucasGandel/ITK,richardbeare/ITK,malaterre/ITK