QtWebEngine for apple M1

[thierry]

Hello,
I'm working on getting my track fully native (aka universal2) on Mac. I'm with Qt 5.15.2.
So I compiled Qt twice: once for x86 and once with the -device-option QMAKE_APPLE_DEVICE_ARCHS=arm64 configure option.
I then used makeuniversal and my binaries and Qt frameworks are universal.. Yay.
Now I tried qtwebengine. So I know that it needs to be on a relatively recent version of chromium, so I took the 5.15 branch and tried to build. With no luck so far. it fails right away by saying the the extensions are not enabled.
So I tried to configure it with ../Qt/bin/qmake . -- -webengine-webrtc -webengine-printing-and-pdf -webengine-pepper-plugins
I also amended the src/buildtools/config/mac_osx.pri
with this:
cross_compile {
GN_TARGET_CPU = $$gnArch($$QT_ARCH)
gn_args += target_cpu="$$GN_TARGET_CPU"
}

so that the args.gn from chromium gets the right arget_cpu.

But then it fails with requiring some .mm file that is indeed not present on disk.

Has somebody had success doing this?