
Build on Linux fails if libfftw3 is not available since commit
a8c1fc92e9
which replaced
pkg_check_modules(FFTW REQUIRED fftw3f)
by
find_package(FFTW REQUIRED)
Fix this build failure by updating FindFFTW.cmake to check for fftw3f
Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>