Re: add order-only-prerequisites example

[Dan Jacobson]

Paul> Sometimes features are advanced enough that providing a simple example

Well still, a few-liner showing how
a: b|c
differs from
a: b c
wouldn't hurt.

Paul> under a public license.

I meant you guys must be reading an O'Reilly book or hung out in Bell
Labs or something.  There's no way I could become a make whiz to the
depths of order-only-prerequisites with just the docs provided. Wait,
I see order-only-prerequisites is of new invention. OK, do provide one
tiny example in the docs, as some of our brains are much more example
oriented than description oriented.

dj> Occasionally, however, you have a situation where you want to impose
dj> a specific ordering on the rules to be invoked _without_ forcing the
dj> target to be updated if one of those rules is executed.  In that case,
dj> you want to define "order-only" prerequisites.

Without plenty of interspersed examples, that still will take deep
concentration to understand, even more if the reader is not a native
English speaker.

Paul> On the off chance you're actually interested in this feature, these
Paul> prerequisites have semantics similar to normal prerequisites: all this
Paul> says is that all of the order-only prerequisites must be built before
Paul> the target that depends on them.  Unlike normal prerequisites, though,
Paul> if one of them is updated that does _NOT_ force the target to rebuild.

OK, I suppose. But a few baby blocks a: b|c examples added to the docs
will drive the point home.