Speeding up plugin builds?

[Joseph Garvin]

Right now if I want to rebuild my plugin, I just type 'make' in the root
build folder. This works fine on a fast PC, but I've been coding on a slower
machine lately, and waiting for make to look through all of the rockbox
sources for changes only to discover that I've just changed a single file
(the .c file for my plugin) is a bit annoying. Is there a way to _only_
rebuild one specified plugin, or at least tell make to only look at plugins
and not all of rockbox?