I am trying to build SDL2 in CMake for iOS on Mac OS X 10.11.6 with Xcode 8.2.1 installed.

I'm using the ios toolchain found here:
https://github.com/leetal/ios-cmake/

Here's my CMake command:
cmake -DCMAKE_TOOLCHAIN_FILE=../games/iOS/ios.toolchain.cmake  ../games
Where ../games is the source directory

I get this CMake configuration error:

CMake Error: The following variables are used in this project, but they are set to NOTFOUND.
Please set them or make sure they are set and tested correctly in the CMake files:
FORCEFEEDBACK
    linked by target "SDL2-static" in directory /Users/steve/Documents/games_ios_build/3rdparty/SDL2/SDL2-2.0.8

-- Configuring incomplete, errors occurred!


This is expected based on Apple's doc indicating it's only part of the macOS SDK:
https://developer.apple.com/documentation/forcefeedback
Compare it to the IOKit Framework, which is listed for both iOS and macOS
https://developer.apple.com/documentation/iokit

When I comment out list(APPEND EXTRA_LIBS ${FORCEFEEDBACK}) for the iOS build, SDL2 built fine so it doesn't even seem to use this library.  Therefore, my suggestion is to omit the library on iOS:

The current code block in the main CMakeLists.txt file:
  if(SDL_FRAMEWORK_FF)
    find_library(FORCEFEEDBACK ForceFeedback)
    list(APPEND EXTRA_LIBS ${FORCEFEEDBACK})
  endif()

After the change:
  if(SDL_FRAMEWORK_FF AND NOT IOS)
    find_library(FORCEFEEDBACK ForceFeedback)
    list(APPEND EXTRA_LIBS ${FORCEFEEDBACK})
  endif()