The FFTW library was developed at MIT by Matteo Frigo and Steven G. Johnson.
The sources are taken from http://www.fftw.org.

This version is not supposed to be configured optimally in the sense of speed.
So if you already have your own installation of FFTW, you should use this one.
It will propably run much faster.

You can easily disable this local version of FFTW by setting the
USE_LOCAL_FFTW to NO (edit the $SRCDIR/*.config.make).

Currently this FFTW version is only used on WINDOWS machines by default. (Take a look at $SRCDIR/WINDOWS.config.make).