Including pybind11 causes Emscripten to fail build

[Edwin F.]

I have a basic QML/C++ Qt app I am able to compile to WebAssembly using Emscripen.
I am trying to use pybind11 on the C++ side so I can embed Python.
It works as expected when I build and execute on my system.

#if defined(_DEBUG)
#undef _DEBUG
#include <Python.h>
#define _DEBUG
#else
#include <Python.h>
#endif
#include <pybind11/embed.h>

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <stdio.h>
#include <iostream>
using namespace std;


void say_something ()
{
    printf ("Say Something nicely\n");
}

static int COUNTER = 0;

void set_counter (int count)
{
    COUNTER = count;
}

struct MyData
{
    float x;
};


struct MyDataPython
{
    float x;
    float y;

    MyDataPython () : x(0), y(0) {}

    MyDataPython (float x, float y) : x(x), y(y) {}


};



PYBIND11_EMBEDDED_MODULE (embeddedmodule, module)
{
    module.doc () = "Embedded Module";
    module.def ("say_something", &say_something);
    module.def ("set_counter", &set_counter);

    pybind11::class_<MyData>(module, "MyData")
            .def_readwrite ("x", &MyData::x);
}


int main(int argc, char *argv[])
{



// TESTING pybind11 stuff here /////////////////////////////////////////////////////////////////////
    pybind11::scoped_interpreter guard{};

    //Python executed
    pybind11::exec ("print('hello world')");
    pybind11::exec ("from test_mod import Test");
    pybind11::exec ("test = Test()");

    pybind11::exec ("import embeddedmodule\nembeddedmodule.say_something()");

    cout << COUNTER << '\n';
    // the import from previous statement still active
    pybind11::exec ("embeddedmodule.set_counter(10)");

    cout << COUNTER << '\n';
////////////////////////////////////////////////////////////////////

        QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

        QGuiApplication app(argc, argv);

        QQmlApplicationEngine engine;
        const QUrl url(QStringLiteral("qrc:/main.qml"));
        QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                         &app, [url](QObject *obj, const QUrl &objUrl) {
            if (!obj && url == objUrl)
                QCoreApplication::exit(-1);
        }, Qt::QueuedConnection);
        engine.load(url);

        return app.exec();

}

When built and executed the simple app launches as expected and I see the following in Application output showing it is working:

08:34:25: Starting /home/thrive/Documents/CODE/QtFORWebAssemblyTest/build-Todo-Desktop_Qt_5_13_2_GCC_64bit-Debug/Todo ...
QML debugging is enabled. Only use this in a safe environment.
hello world
init TEST class!
Say Something nicely
0
10

But when I try to build/make this same app using Emscripten it fails:

ed@machine:~/Documents/CODE/QtFORWebAssemblyTest/Todo/build$ /home/thrive/Qt/5.13.2/wasm_32/bin/qmake ..
Project MESSAGE: Setting TOTAL_MEMORY to 64MB

ed@machine:~/Documents/CODE/QtFORWebAssemblyTest/Todo/build$ make

em++ -c -pipe -O3 -std=gnu++11 -s ALLOW_MEMORY_GROWTH=1 -s TOTAL_MEMORY=64MB -Wall -W -DQT_DEPRECATED_WARNINGS -DQT_NO_DEBUG -DQT_QUICK_LIB -DQT_GUI_LIB -DQT_QML_LIB -DQT_NETWORK_LIB -DQT_CORE_LIB -I../../Todo -I. -I/usr/include/python3.6m -I/home/thrive/Downloads/pybind11/include -I/home/thrive/Qt/5.13.2/wasm_32/include -I/home/thrive/Qt/5.13.2/wasm_32/include/QtQuick -I/home/thrive/Qt/5.13.2/wasm_32/include/QtGui -I/home/thrive/Qt/5.13.2/wasm_32/include/QtQml -I/home/thrive/Qt/5.13.2/wasm_32/include/QtNetwork -I/home/thrive/Qt/5.13.2/wasm_32/include/QtCore -I. -I/home/thrive/.emscripten_ports/openssl/include -I/home/thrive/Qt/5.13.2/wasm_32/mkspecs/wasm-emscripten -o main.o ../main.cpp
In file included from ../main.cpp:6:
In file included from /usr/include/python3.6m/Python.h:8:
/usr/include/python3.6m/pyconfig.h:104:3: error: unknown multiarch location for pyconfig.h
# error unknown multiarch location for pyconfig.h
  ^
In file included from ../main.cpp:6:
In file included from /usr/include/python3.6m/Python.h:53:
In file included from /usr/include/python3.6m/pyport.h:4:
/usr/include/python3.6m/pyconfig.h:104:3: error: unknown multiarch location for pyconfig.h
# error unknown multiarch location for pyconfig.h
  ^
In file included from ../main.cpp:6:
In file included from /usr/include/python3.6m/Python.h:53:
/usr/include/python3.6m/pyport.h:686:2: error: "LONG_BIT definition appears wrong for platform (bad gcc/glibc config?)."
#error "LONG_BIT definition appears wrong for platform (bad gcc/glibc config?)."
 ^
In file included from ../main.cpp:6:
In file included from /usr/include/python3.6m/Python.h:76:
In file included from /usr/include/python3.6m/pymath.h:4:
/usr/include/python3.6m/pyconfig.h:104:3: error: unknown multiarch location for pyconfig.h
# error unknown multiarch location for pyconfig.h
  ^
In file included from ../main.cpp:6:
In file included from /usr/include/python3.6m/Python.h:77:
In file included from /usr/include/python3.6m/pytime.h:5:
/usr/include/python3.6m/pyconfig.h:104:3: error: unknown multiarch location for pyconfig.h
# error unknown multiarch location for pyconfig.h
  ^
In file included from ../main.cpp:6:
In file included from /usr/include/python3.6m/Python.h:89:
/usr/include/python3.6m/unicodeobject.h:68:2: error: Must define SIZEOF_WCHAR_T
#error Must define SIZEOF_WCHAR_T
 ^
In file included from ../main.cpp:8:
In file included from /home/thrive/Downloads/pybind11/include/pybind11/embed.h:12:
In file included from /home/thrive/Downloads/pybind11/include/pybind11/pybind11.h:45:
In file included from /home/thrive/Downloads/pybind11/include/pybind11/attr.h:13:
In file included from /home/thrive/Downloads/pybind11/include/pybind11/cast.h:16:
/home/thrive/Downloads/pybind11/include/pybind11/detail/internals.h:264:45: error: use of undeclared identifier
      'PyGILState_Ensure'
        gil_scoped_acquire_local() : state (PyGILState_Ensure()) {}
                                            ^
/home/thrive/Downloads/pybind11/include/pybind11/detail/internals.h:265:39: error: use of undeclared identifier
      'PyGILState_Release'
        ~gil_scoped_acquire_local() { PyGILState_Release(state); }
                                      ^
In file included from ../main.cpp:8:
In file included from /home/thrive/Downloads/pybind11/include/pybind11/embed.h:12:
/home/thrive/Downloads/pybind11/include/pybind11/pybind11.h:2182:28: warning: unused variable 'gil' [-Wunused-variable]
        gil_scoped_acquire gil;
                           ^
1 warning and 8 errors generated.
shared:ERROR: compiler frontend failed to generate LLVM bitcode, halting
Makefile:792: recipe for target 'main.o' failed
make: *** [main.o] Error 1

When I remove these two includes from main.cpp and remove all the pybind11 code, it builds using Emscripten, so it is failing because these two includes:

#include <Python.h>
#include <pybind11/embed.h>

Here is my .pro

QT += quick
CONFIG += c++11

# The following define makes your compiler emit warnings if you use
# any Qt feature that has been marked deprecated (the exact warnings
# depend on your compiler). Refer to the documentation for the
# deprecated API to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS

# You can also make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

SOURCES += \
        main.cpp \

RESOURCES += qml.qrc

# Additional import path used to resolve QML modules in Qt Creator's code model
QML_IMPORT_PATH =

# Additional import path used to resolve QML modules just for Qt Quick Designer
QML_DESIGNER_IMPORT_PATH =

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

QMAKE_WASM_TOTAL_MEMORY=64MB


LIBS += -L /usr/local/lib/python3.6m -lpython3.6m

INCLUDEPATH += /usr/include/python3.6m \
                /home/thrive/Downloads/pybind11/include

DEPENDPATH += /usr/include/python3.6m

Anyone have any ideas on how to resolve this? Essentially the problem is including 'Python.h' and 'pybind11