MKREPRO: what variable contains the actual obj directory?

[Thomas Klausner <wiz%NetBSD.org@localhost>]

Hi!

For reproducible builds, the binaries should be the same independent
of the paths where the source or object directories live.

There are patches available for gcc to fix the paths (i.e., replace
the obj directory that is actually used in a build with a fixed
string, e.g. /usr/obj).

However, with the gazillion options we have in share/mk for choosing
object directories, I don't know what variable contains the actual
object directory that is used during a build.

Can someone shed a light on this?
 Thomas