Description of problem:
find_package (FFTW3) in CMakeLists.txt will generate the error message:

CMake Error at /usr/lib64/cmake/fftw3/FFTW3Config.cmake:13 (include):
  include could not find load file:
 /usr/lib64/cmake/fftw3/FFTW3LibraryDepends.cmake


Version-Release number of selected component (if applicable):
Name         : fftw-devel
Version      : 3.3.8
Release      : 4.fc30
Architecture : i686
Size         : 130 k
Source       : fftw-3.3.8-4.fc30.src.rpm


How reproducible: always


Steps to Reproduce:
1. Use the line find_package (FFTW3) in *any* CMakeLists.txt

Actual results: 
CMake Error at /usr/lib64/cmake/fftw3/FFTW3Config.cmake:13 (include):
  include could not find load file:
 /usr/lib64/cmake/fftw3/FFTW3LibraryDepends.cmake


Expected results:
It should work. ;-)

Additional info:
When I build fftw-3.3.8 from source from http://www.fftw.org/download.html
via cmake, ninja, and ninja install (I presume make works just as well) in default configuration, cmake generates additional files
$(CMAKE_INSTALL_PREFIX)/lib64/cmake/fftw3/FFTW3LibraryDepends.cmake
$(CMAKE_INSTALL_PREFIX)/lib64/cmake/fftw3/FFTW3LibraryDepends-release.cmake

These should probably be included in the fftw-devel package as well?