The CComplex library is licensed under a two-clause BSD license that
should let you do pretty much anything.  See TWO-CLAUSE-BSD.txt.

The interface to FFTW is useless without linking to the FFTW, which is
publically available as GPL.  Since I don't want to argue about whether
it is a derived work, I've just made it available under the GPL (see
GPL.txt).  If you have bought a different license from MIT, or another
library develops with the same interface, I might reconsider.