win32 dependency generation

I just checked in a change to enable auto-deps for the win32 build (bug 
167442).  This means that dependencies for a source file will be 
generated when the file is compiled instead of requiring a separate 
build phase.  This is the same default that the unix & mac gmake builds 
use.

On average, this will speed up depend builds.  However, it will slowdown 
clobber-only builds as you will be unnecessarily doing the equivalent of 
a depend step.  You can disable this feature and return to the manual 
dependency method by using --disable-auto-deps.

With auto-deps enabled, it is safe to just use client.mk's build_all 
target, which enforces tier-level module dependencies (see bug 107302), 
in lieu of the alldep target.

- cls