nvme.c:2012:2: error: call to undeclared function 'memmove'

My kernel build started failing recently with the following error. I use 
a custom kernel config but looking at NOTES, it's not clear that I've 
missed an option that would make it compile.

In file included from /usr/src/sys/dev/nvme/nvme_util.c:34:
/usr/src/sys/dev/nvme/nvme.h:2012:2: error: call to undeclared function 
'memmove'; ISO C99 and later do not support implicit function 
declarations [-Werror,-Wimplicit-function-declaration]
  2012 |         memmove(sn, cdata->sn, NVME_SERIAL_NUMBER_LENGTH);
       |         ^
1 error generated.
*** Error code 1

I've also tried compiling after blowing away usr/obj.

Ian