Failed to compile XNNPACK with Emscripten

Hello,

According to documentation XNNPACK should be compilable with emscripten sdk.

But why it is failing for me when i include XNNPACK cmake to my project?

CMake Error at third_party/xnnpack/CMakeLists.txt:359 (MESSAGE):
  Unrecognized CMAKE_SYSTEM_NAME value "Emscripten"
