DF-2908 PoC build log (in-guest DragonFly cc 8.3 [DragonFly] Release/2019-02-22)

$ cc -O2 -pthread -Wall -o /tmp/df2908 /tmp/varsym_exit_race.c
(no warnings, no errors)
BUILD_OK
-rwxr-xr-x 1 root wheel 9488 Sep  3 06:03 /tmp/df2908

(Note: first compile attempt failed with `unknown type name 'sig_atomic_t'`;
fixed by adding #include <signal.h> to the PoC — that is the only change vs
the original draft. Rebuilt clean on stock kernel #0 and again on patched
kernel #1.)

Fix kernel build (validation):
$ cd /usr/src && git apply /tmp/fix.diff && make nativekernel
...
>>> Kernel build for X86_64_GENERIC completed on Thu Sep  3 06:31:46 UTC 2026
$ make installkernel
>>> Kernel install for X86_64_GENERIC completed on Thu Sep  3 06:54:25 UTC 2026
$ reboot  ->  DragonFly 6.5-DEVELOPMENT #1: Thu Sep  3 06:18:40 UTC 2026
(config X86_64_GENERIC has `options INVARIANTS' at sys/config/X86_64_GENERIC:56)