Fix FFTW unit test with clang
(grafted from 4372c66911396e2eea1d5a817c0c5dd3cfba849c)

--HG--
branch : 3.2
extra : source : 4372c66911396e2eea1d5a817c0c5dd3cfba849c
Fix sparse_product/sparse_extra unit tests
(grafted from 8a49bc0c5e2ea73ee6bd044d04af09fc38d33451)

--HG--
branch : 3.2
extra : source : 8a49bc0c5e2ea73ee6bd044d04af09fc38d33451