cmake: use SDL_CPU_ARM32 instead of CMAKE_GENERATOR_PLATFORM STREQUAL "ARM"

CMakeLists.txt

@@ -1766,7 +1766,7 @@ elseif(WINDOWS)
     check_include_file(ddraw.h HAVE_DDRAW_H)
     check_include_file(dsound.h HAVE_DSOUND_H)
     check_include_file(dinput.h HAVE_DINPUT_H)
-    if(WINDOWS_STORE OR CMAKE_GENERATOR_PLATFORM STREQUAL "ARM")
+    if(WINDOWS_STORE OR SDL_CPU_ARM32)
       set(HAVE_DINPUT_H 0)
     endif()
     check_include_file(dxgi.h HAVE_DXGI_H)
@@ -3368,7 +3368,7 @@ if(SDL_SHARED)
       OUTPUT_NAME "SDL2")
   endif()
   # Note: The clang toolset for Visual Studio does not support /NODEFAULTLIB.
-  if(MSVC AND NOT SDL_LIBC AND NOT MSVC_CLANG AND NOT CMAKE_GENERATOR_PLATFORM STREQUAL "ARM")
+  if(MSVC AND NOT SDL_LIBC AND NOT MSVC_CLANG AND NOT SDL_CPU_ARM32)
     # Don't try to link with the default set of libraries.
     if(NOT WINDOWS_STORE)
       set_property(TARGET SDL2 APPEND_STRING PROPERTY LINK_FLAGS " /NODEFAULTLIB")