This is xnu-4903.221.2. See this file in:
Directory listing for xnu-4903.221.2//libkern
.clang-format
Makefile
OSKextLib.cpp
OSKextVersion.c
c++/
conf/
crypto/
firehose/
gen/
img4/
kernel_mach_header.c
kmod/
kxld/
libclosure/
libkern/
mkext.c
net/
os/
stack_protector.c
stdio/
uuid/
zlib/