Hi,
clock_gettime should work on any modern system out of the box: linux - C++ error: undefined reference to 'clock_gettime' and 'clock_settime' - Stack Overflow
Although there seems to have been some issue with that timer and MinGW: Bug #1853168 “undefined reference to `clock_gettime'” : Bugs : EPICS Base
Could you try to find what MinGW version you have?
Also you could edit timing.c and timing.h to just return 0, if you want to use acados without timings.
Best,
Jonathan