Userspace cores seem to work:
```
$ sysctl kern. | grep compress
kern.compress_user_cores_zstdlevel: 6
kern.compress_user_cores: 1
$ sysctl kern.corefile
kern.corefile: %N.core
$ python2 -c 'import os; os.abort()'
[1] 1156 abort (core dumped) python2 -c 'import os; os.abort()'
$ ls -l python2.7.core.zst
-rw------- 1 conrad conrad 429K Nov 15 12:17 python2.7.core.zst
$ zstd --test ./python2.7.core.zst
./python2.7.core.zst: 12894208 bytes
$ echo $(( 12894208 / 1024 ))
12592
$ echo $(( 100 * 429 / 12592 ))
3 # compressed size as percent of uncompressed core size
$ zstd -d ./python2.7.core.zst
./python2.7.core.zst: 12894208 bytes
$ file python2.7.core
python2.7.core: ELF 64-bit LSB core file x86-64, version 1 (FreeBSD), FreeBSD-style, from ' -c import os; os.abort()'
```
Kernel dumps (testing in progress):
```
$ dumpon -l
gpt/freebsd-swap
$ sysctl debug.{trace,debugger}_on_panic debug.minidump
debug.trace_on_panic: 1
debug.debugger_on_panic: 1
debug.minidump: 1
$ sysctl kern.kerneldump_zstdlevel
kern.kerneldump_zstdlevel: 6
$ sudo sysctl debug.kdb.panic=1
...
```