- update to 3.3.6-pl2
* Bugfix: MPI Fortran-03 headers were missing in FFTW 3.3.6-pl1.
* 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.*.
* 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)

(FATE#321716).