* anchor search strings appropriately,
* use .ALLSRC to pass the full path to the D script to dtrace(1),
* don't insert the auto-generated header into SRCS - it doesn't
accomplish anything, and we end up having to remove it from OBJS anyway.
Reviewed by: rpaulo
Differential Revision: https://reviews.freebsd.org/D978
MFC after: 3 weeks
Sponsored by: EMC / Isilon Storage Division