cmake: Add the IoRing async i/o code to the Windows build.

The Visual Studio projects have been compiling this for awhile, but apparently
we haven't tested this through CMake before. Toolchains without access to
the latest Windows 11 SDK headers have been preprocessing out the dependency
on this code, so we never noticed.

CMakeLists.txt

@@ -1889,6 +1889,7 @@ elseif(WINDOWS)
 
   sdl_glob_sources("${SDL3_SOURCE_DIR}/src/core/windows/*.c")
   sdl_glob_sources("${SDL3_SOURCE_DIR}/src/main/windows/*.c")
+  sdl_glob_sources("${SDL3_SOURCE_DIR}/src/io/windows/*.c")
 
   if(TARGET SDL3-shared AND MSVC AND NOT SDL_LIBC)
     # Prevent codegen that would use the VC runtime libraries.