SDL2 support runs at half of the monitor refresh rate under Wayland

[santiagocezar]

When running the sdl2_01_basic example with the env variable SDL_VIDEODRIVER set to wayland (after disabling both "bundled" and the "static-link" features, otherwise it wont compile), the applications noticeably runs slower, and according to imgui.io().framerate, exactly at half the refresh rate of the monitor.

I can reproduce this on the latest commit at the time 9009022, on GNOME Wayland.

$ sdl2-config --version
2.26.4
$ mutter --version
mutter 43.3
$ rustc --version
rustc 1.68.0