make(1): Create two more custom variables to speed up dports

make(1): Create two more custom variables to speed up dports

I've added two new static values to bmake:

.MAKE.DF.OSREL
This will currently return "4.5"

.MAKE.DF.VERSION
This will currently return "400500".  It matches what was in place on
/usr/src/sys/sys/param.h during the last buildworld.

Every dport runs piped shell commands to get these values. After iterating
through the entire ports tree several times, I noticed a large presence
of awk in process list.  After modifying bmake and then modifying dports
locally, the iteration runs 15% faster.  There are other optimizations
that can be done, but that's out of scope of this commit.