This is xnu-8019. See this file in:
Directory listing for xnu-8019//libkern
Makefile
OSKextLib.cpp
OSKextVersion.c
amfi/
apple_encrypted_archive/
c++/
conf/
coreanalytics/
coretrust/
crypto/
firehose/
gen/
img4/
kernel_mach_header.c
kmod/
kxld/
libclosure/
libkern/
mkext.c
net/
os/
ptrauth_utils.c
stack_protector.c
stdio/
uuid/
zlib/