make: for loop gotchas (was: make: dealing with targets with multiple outputs)

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

SJG> considering that .for loops introduce their own side effects
SJG> I prefer to avoid them when unnecessary.

DH> They are by far the best (most flexible, least arbitrary gotchas)
DH> choice for complex makefiles.
Using .for loops heavily, I have to add that apparently a lot of progress 
has been "recently" made in that area. I have terrible work-arounds (and 
comments to that effect) in ten-year-old Makefiles that aren't needed any more.
I guess that's mostly dholland@'s work, thanks.