Incorporate the `Xchg` operation

1 job for master in 15 minutes and 52 seconds (queued for 16 seconds)
Name Stage Failure
failed Build
make[2]: Target 'real-all' not remade because of errors.
make[1]: *** [Makefile.coq:343: all] Error 2
make: *** [Makefile:3: all] Error 2

real 0m7.113s
user 0m29.006s
sys 0m4.504s
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1