Full untrimmed compiler + runtime output from the DragonFly guest.

Attempt 1 (seed PoC as written — failed, missing errno.h):
  $ cc -O -Wall -o /tmp/poc /tmp/poc.c -lpthread
  /tmp/poc.c: In function 'main':
  /tmp/poc.c:110:16: error: 'errno' undeclared (first use in this function)
                 strerror(errno));
                  ^~~~~~
  /tmp/poc.c:110:16: note: 'errno' is defined in header '<errno.h>'; did you forget to '#include <errno.h>'?
  /tmp/poc.c:46:1:
  +#include <errno.h>
  /tmp/poc.c:110:16: note: each undeclared identifier is reported only once for each function
  run_rc=1

Fix applied: added #include <errno.h>.

Attempt 2 (final, successful build):
  $ cc -O -Wall -o /tmp/poc /tmp/poc.c -lpthread
  BUILD_OK