em++ mandelbrot.cpp -s WASM=1 -o mandelbrot.js
WARNING  root: Assigning a non-existent settings attribute "WASM"
WARNING  root:  - did you mean one of ASM_JS?
WARNING  root:  - perhaps a typo in emcc's  -s X=Y  notation?
WARNING  root:  - (see src/settings.js for valid values)
In file included from mandelbrot.cpp:16:
In file included from /usr/share/emscripten/system/include/emscripten/bind.h:10:
In file included from /usr/share/emscripten/system/include/emscripten/val.h:4:
/usr/share/emscripten/system/include/emscripten/wire.h:24:5: error: unknown type
      name 'constexpr'
    constexpr bool has_unbound_type_names = true;
    ^
/usr/share/emscripten/system/include/emscripten/wire.h:24:15: error: expected
      unqualified-id
    constexpr bool has_unbound_type_names = true;
              ^
/usr/share/emscripten/system/include/emscripten/wire.h:39:20: error: unknown
      type name 'constexpr'
            static constexpr TYPEID get() {
                   ^
/usr/share/emscripten/system/include/emscripten/wire.h:39:36: error: expected
      ';' at end of declaration list
            static constexpr TYPEID get() {
                                   ^
/usr/share/emscripten/system/include/emscripten/wire.h:54:20: error: unknown
      type name 'constexpr'
            static constexpr TYPEID get() {
                   ^
/usr/share/emscripten/system/include/emscripten/wire.h:54:36: error: expected
      ';' at end of declaration list
            static constexpr TYPEID get() {
                                   ^
/usr/share/emscripten/system/include/emscripten/wire.h:63:9: error: unknown type
      name 'constexpr'
        constexpr TYPEID getLightTypeID(const T& value) {
        ^
/usr/share/emscripten/system/include/emscripten/wire.h:63:25: error: expected
      ';' at end of declaration
        constexpr TYPEID getLightTypeID(const T& value) {
                        ^
/usr/share/emscripten/system/include/emscripten/wire.h:63:47: error: unknown
      type name 'T'
        constexpr TYPEID getLightTypeID(const T& value) {
                                              ^
/usr/share/emscripten/system/include/emscripten/wire.h:63:26: error: C++
      requires a type specifier for all declarations
        constexpr TYPEID getLightTypeID(const T& value) {
                         ^
/usr/share/emscripten/system/include/emscripten/wire.h:64:44: error: use of
      undeclared identifier 'T'
            typedef typename Canonicalized<T>::type C;
                                           ^
/usr/share/emscripten/system/include/emscripten/wire.h:64:48: error: definition
      or redeclaration of 'type' cannot name the global scope
            typedef typename Canonicalized<T>::type C;
                                             ~~^
/usr/share/emscripten/system/include/emscripten/wire.h:64:48: error: typedef
      declarator cannot be qualified
            typedef typename Canonicalized<T>::type C;
                                             ~~^
/usr/share/emscripten/system/include/emscripten/wire.h:64:52: error: expected
      ';' at end of declaration
            typedef typename Canonicalized<T>::type C;
                                                   ^
/usr/share/emscripten/system/include/emscripten/wire.h:65:21: error: use of
      undeclared identifier 'has_unbound_type_names'
            return (has_unbound_type_names || std::is_polymorphic<C>::value)
                    ^
/usr/share/emscripten/system/include/emscripten/wire.h:65:67: error: use of
      undeclared identifier 'C'
            return (has_unbound_type_names || std::is_polymorphic<C>::value)
                                                                  ^
/usr/share/emscripten/system/include/emscripten/wire.h:67:31: error: use of
      undeclared identifier 'T'
                : LightTypeID<T>::get();
                              ^
/usr/share/emscripten/system/include/emscripten/wire.h:72:20: error: unknown
      type name 'constexpr'
            static constexpr TYPEID get() {
                   ^
/usr/share/emscripten/system/include/emscripten/wire.h:72:36: error: expected
      ';' at end of declaration list
            static constexpr TYPEID get() {
                                   ^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.
ERROR    root: compiler frontend failed to generate LLVM bitcode, halting
hyperion@hyperion:~/tools/playground/example_codelab/mandelbrot-simple$