As near as I can tell, Spice 0.12.6 will make absolutely no use of this callback, so my primitive understanding is that it should be safe to just compile out on newer spice versions.
(Or at least, it will be functionally identical to what already happens in practice on such compilations.) The point, as always, is to test people's patience with me checking in patches to make the Clang build happy on modern Linux distributions. The .set_mm_time method was marked as DEPRECATED, so the famously picky Clang compiler will error out now. John Snow (1): spice: avoid .set_mm_time on >= 0.12.6 hw/display/qxl.c | 4 ++++ include/ui/qemu-spice.h | 3 +++ ui/spice-display.c | 4 ++++ 3 files changed, 11 insertions(+) -- 2.5.5