cmake,emscripten and c++17

Trying to compile my c++17 based project (using entt) makes problems with using my urho3d-docker-web-image that uses emscripten for compilation to web.

emcc (Emscripten gcc/clang-like replacement) 1.39.8 ((unknown revision))

Using (I'm mainly using gcc for compilation, android uses clang afaik?)

target_compile_features(${PROJECT_NAME} PUBLIC cxx_std_17)

leads to an error like that:

CMake Error at CMakeLists.txt:95 (target_compile_features):
  target_compile_features no known features for CXX compiler

  "Clang"

  version 1.39.8.

I tried a couple of approaches, but the only one that worked for me was a 'brutal' add_definitions(..)

add_definitions(-std=c++1z -std=gnu++1z)

I didn't dig too deep into the problem...but for now it works... ;)