meson: Correctly set DDXOSVERRORF and DDXBEFORERESET on xwin

This worked with autotools, but not meson build system.

Signed-off-by: Povilas Kanapickas <povilas@radix.lt>
(cherry picked from commit 04c93b98)
5 jobs for server-21.1-backports in 4 minutes and 58 seconds (queued for 10 seconds)