cmake: detect Emscripten architecture as emscripten

cmake/CheckCPUArchitecture.cmake

@@ -34,6 +34,8 @@ function(check_cpu_architecture ARCH VARIABLE)
     _internal_check_cpu_architecture("defined(__aarch64__) || defined(_M_ARM64)" arm64 ${VARIABLE})
   elseif(ARCH STREQUAL "loongarch64")
     _internal_check_cpu_architecture("defined(__loongarch64)" loongarch64 ${VARIABLE})
+  elseif(ARCH STREQUAL "emscripten")
+    _internal_check_cpu_architecture("defined(__EMSCRIPTEN__)" emscripten ${VARIABLE})
   else()
     message(WARNING "Unknown CPU architectures (${ARCH}).")
     set(${VARIABLE} FALSE)

cmake/sdlplatform.cmake

@@ -52,6 +52,8 @@ macro(SDL_DetectCMakePlatform)
     set(SDL_CMAKE_PLATFORM Minix)
   elseif(CMAKE_SYSTEM_NAME MATCHES "Android.*")
     set(SDL_CMAKE_PLATFORM Android)
+  elseif(CMAKE_SYSTEM_NAME MATCHES "Emscripten.*")
+    set(SDL_CMAKE_PLATFORM Emscripten)
   elseif(CMAKE_SYSTEM_NAME MATCHES "BeOS.*")
     message_error("BeOS support has been removed as of SDL 2.0.2.")
   endif()
@@ -76,7 +78,7 @@ function(SDL_DetectCPUArchitecture)
     endforeach()
   endif()
 
-  set(sdl_known_archs x86 x64 arm32 arm64 loongarch64)
+  set(sdl_known_archs x86 x64 arm32 arm64 loongarch64 emscripten)
   if(NOT sdl_cpu_names)
     set(found FALSE)
     foreach(sdl_known_arch ${sdl_known_archs})