Check for GLsync before using it
Copy what we do in GTK4: Check for GL>=3.2 or GLES>3.0 or the GL_ARB_sync extension. And then store that info for a (private) gdk_gl_context_has_sync() function. And then check that function before using GLsync objects as introduced by commit 98114859.
Fixes #5749 (closed)
Edited by Benjamin Otte