Add iOS cross-compiling documentation to the cmake-toolchains guide
The cross-compilation guide at https://cmake.org/cmake/help/latest/manual/cmake-toolchains.7.html#cross-compiling is getting better and better, but it still misses instructions to build for iOS (e.g. iphone and iphone simulator).
I guess most people will use the Xcode generator when building for those targets so specific instructions for this generator might be a nice addition as well.
Most of what I can find on the Internet recommend using the toolchain file https://github.com/cristeab/ios-cmake but it does feel a bit of a hack (it is trying to force the compiler to gcc, which does not work and is deprecated, it by passes the compiler checks...). I also found good information in the following thread: https://cmake.org/pipermail/cmake-developers/2015-December/027260.html
Basically, it would be nice to have an official CMake guide when targetting iOS. A support as good as the brand new Android work would be awesome!