The version in Ubuntu 22.04 comes without `ConvertUTF.{h,c}`.
We actually do not need `ConvertUTF.{h,c}` and starting from
v4.19 it is possible to tell SimpleIni to not include it
by setting `SI_NO_CONVERSION`.
Sets `SI_NO_CONVERSION` and raises the minimum required SimpleIni
version to 4.19.
1. Platform and toolchain files are now all under `platforms/`, with a
single `CMake/platforms/${platform}.cmake` per platform.
2. Custom functions/macros are under `functions/`.
3. Finder modules are in `/finders`.