On CMake v3.28+, `EXCLUDE_FROM_ALL` is supported natively as an argument
to `FetchContent_Declare`.
On CMake v3.30+, `FetchContent_Populate`, which we use to polyfill
`EXCLUDE_FROM_ALL` support for older versions of CMake, is deprecated
and triggers a noisy warning.
Avoids the warning by using the native `EXCLUDE_FROM_ALL` support on
CMake v3.28+.
With this flag (off by default), all of the dependencies are packaged
into the source archive (including SDL2 etc).
Useful for building on machines without an internet connection.
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`.