make: dealing with targets with multiple outputs

[Simon J Gerraty <sjg%juniper.net@localhost>]

A common gripe about make is how it handles (or doesn't depending on
pov) targets that generate multiple outputs.
The classic case being yacc but there are far worse examples.

I was discussing this with bdrewery at last BSDCan, and came up with the
idea of a new special src to mark a set of targets as being a unit.
Eg.

foo.c foo.h: foo.y .NAMING_STUFF_IS_HARD

The intent being that if any of the targets are out-of-date or missing
the script for just one (the first one would be an obvious choice)
should be run, and when it is marked up to date so are it's companions.

This would require yet another Lst in GNode.

Thoughts?
[my subscription might be busted so cc welcome]