cross compile flag in Makefile?

[matthew sporleder <msporleder%gmail.com@localhost>]

pkgsrc cross-compile (target arm from your amd64, for example) has
been coming up again and I would like to revive the idea of flagging
cross-compile friendly packages in their Makefile.

Something along the lines of:
CROSS_TARGETS or even CROSS_FRIENDLY

I feel like this was brought up before but didn't get much traction.
What are the philosophies on this?

Matt