Resolving dependencies...
Error: cabal: Could not resolve dependencies:
[__0] trying: patch-image-0.3.3.2 (user goal)
[__1] trying: patch-image:+llvm
[__2] trying: comfort-fftw-0.0.0.1 (dependency of patch-image +llvm)
[__3] next goal: fftw-ffi (dependency of comfort-fftw)
[__3] rejecting: fftw-ffi-0.1, fftw-ffi-0.0 (conflict: pkg-config package
fftw3>=3.3 && <4, not found in the pkg-config database)
[__3] fail (backjumping, conflict set: comfort-fftw, fftw-ffi)
After searching the rest of the dependency tree exhaustively, these were the
goals I've had most trouble fulfilling: patch-image, fftw-ffi,
patch-image:llvm, comfort-fftw
Try running with --minimize-conflict-set to improve the error message.