Where/how gets the PDE Build the target platform plugins?

Where/how gets the PDE Build the target platform plugins?

i've inherited an Eclipse RCP Project from a colleague who left the
company. Along with the project comes the pde build setup, which i don't
quite get. During development of the latest release, i need to add another
plugin (org.eclipse.compare...). I added it to the target platform and
keept programming. But there are now problems with the build. The finished
product doesn't contain the added plugin .jar. How can i change the build,
so that the jar is added? I'm grateful for any hints. Followed a few clues
while seraching through the build files, but that turnend up nothing.