No X11 libraries, therefore no GLX and MESA is compiled without OpenGL support and only GLES2 support (libepoxy was patched to compile under these circumstances by applying the for instance https://github.com/anholt/libepoxy/pull/80 - but that shouldn't affect the matter at hand).

libepoxy also had another bug, which would fail to report the correct value from epoxy_egl_get_current_gl_context_api (s.a. https://github.com/anholt/libepoxy/pull/90). Consequential attempts to load libGL.so would crash any GTK program. For the sake of testing GLES2 capabilities, epoxy_egl_get_current_gl_context_api was modified and hardcoded to return EGL_OPENGL_ES_API to the effect that GTK/epoxy would no longer attempt to load libGL.so - (hopefully), this shouldn't affect the matter at hand, either.

Then, with, for example WebkitGTK+ / MiniBrowser starting the program does succeed (in the sense that it does not crash due to missing libGL.so). It also seems to be able to render pages.

However (for example), right clicking on the page to bring up the context menu will terminate the program with

Gdk-ERROR **: Error flushing display: Broken pipe.

The backtrace is inconclusive as far as I can see, from bottom to top:

main -> gtk_main -> g_main_loop_run -> ?? (glib) -> g_main_context_prepare -> gdk_event_source_prepare(wayland/gdkeventsource.c:66) -> g_log ...