Quicker re-build after patching

Hi,

Whenever I make a change to the Mozilla code (or apply a patch), I
re-build the project using:

make -f client.mk build

This works, but takes several minutes, and appears to be doping a lot
more than just re-compiling the C++ files that I changed and re-linking
(in fact, even if I changed nothing, it still takes several minutes).

Is there an easy way to just compile the changed files, without running
all these "nsinstall"s (whatever they are)?

TIA,

- Uri.