webkitgtk does not build anymore / EGL_WAYLAND_BUFFER

[wwwutz]

/dev/shm/mxqd/mnt/job/19296063/webkitgtk-2.27.3-1/buildroot/webkitgtk/webkitgtk-2.27.3-1/source/Source/WebKit/UIProcess/gtk/WaylandCompositor.cpp:134:116: error: use of undeclared identifier 'EGL_WAYLAND_BUFFER_WL'
    return static_cast<EGLImageKHR*>(eglCreateImage(PlatformDisplay::sharedDisplay().eglDisplay(), EGL_NO_CONTEXT, EGL_WAYLAND_BUFFER_WL, m_resource, nullptr));
                                                                                                                   ^
4 warnings and 1 error generated.

[wwwutz]

fixed by #1649 and finalized by #1650