Details:
PiZeroW
Linux XXX 4.14.98+ #1200 Tue Feb 12 20:11:02 GMT 2019 armv6l GNU/Linux
Latest kernel-headers
Added rpi-source

I get this error compiling on PiZeroW

~/WireGuard/src# make
  CC [M]  /root/WireGuard/src/main.o
  CC [M]  /root/WireGuard/src/noise.o
  CC [M]  /root/WireGuard/src/device.o
/root/WireGuard/src/device.c: In function 'wg_xmit':
/root/WireGuard/src/device.c:165:3: error: implicit declaration of function
'skb_mark_not_on_list' [-Werror=implicit-function-declaration]
   skb_mark_not_on_list(skb);
   ^~~~~~~~~~~~~~~~~~~~
cc1: some warnings being treated as errors
scripts/Makefile.build:326: recipe for target
'/root/WireGuard/src/device.o' failed
make[2]: *** [/root/WireGuard/src/device.o] Error 1
Makefile:1535: recipe for target '_module_/root/WireGuard/src' failed
make[1]: *** [_module_/root/WireGuard/src] Error 2
Makefile:37: recipe for target 'module' failed
make: *** [module] Error 2

TIA for any insights. Robert