emscan-deps can't find port headers

Related to #24454 with #24506 emscan-deps can't find the port headers probably because it's not invoking the setup steps that emcc would've done in a later step.
```cmake
[build] "/mnt/e/Workspace/SDLTemplate/.cache/emsdk/upstream/emscripten/emscan-deps" -format=p1689 -- /mnt/e/Workspace/SDLTemplate/.cache/emsdk/upstream/emscripten/em++ -DPROJECT_ID=\"dev.sdl.hello\" -DPROJECT_NAME=\"HelloSDL\" -DPROJECT_VERSION=\"0.0.1\" -stdlib=libc++ -stdlib=libc++ -g -std=gnu++23 -fPIE -sUSE_SDL=3 -x c++ /mnt/e/Workspace/SDLTemplate/Source/App.ixx -c -o CMakeFiles/HelloSDL.dir/Source/App.ixx.o -MT CMakeFiles/HelloSDL.dir/Source/App.ixx.o.ddi -MD -MF CMakeFiles/HelloSDL.dir/Source/App.ixx.o.ddi.d > CMakeFiles/HelloSDL.dir/Source/App.ixx.o.ddi.tmp && mv CMakeFiles/HelloSDL.dir/Source/App.ixx.o.ddi.tmp CMakeFiles/HelloSDL.dir/Source/App.ixx.o.ddi
[build] Error while scanning dependencies for /mnt/e/Workspace/SDLTemplate/Source/App.ixx:
[build] /mnt/e/Workspace/SDLTemplate/Source/App.ixx:6:10: fatal error: 'SDL3/SDL.h' file not found
```