Process target only if prerequisite was processed?

[Matt Perry]

Is there a way to tell make to only process a target if one or more of its 
prerequisites was processed?  Let's say I have a make file like this fake 
one here:

all: prereq1 prereq2
        do something
prereq1:
        ...
prereq2:
        ...

In this case an action needs to be taken if either one of the 
prerequisites were processed.  The "all" target doesn't generate a file.  
It just runs a program.

-- 
Matt Perry | matt at primefactor dot com