awk: merge fixes to metamode

This is a partial MFC of c63c5ab001106/r349062. The whole thing doesn't
apply cleanly, but this bit, at least, is needed to fix metamode on
stable/12 after the changes to awk were merged from head. Rather than
risk breaking other things, I'm just merging the bit I know that's
needed. All build tools need to be in DEPENDOBJ so the dependency order
is correct and they get built with host tools.

Reported by: kp
Sponsored by: Netflix