I encountered a couple of things that broke after Ian's previous
patch: one was my nightly build scripts that use 'make stage=2' at the
top level, and the other is 'make fast' in libraries/base, which uses
'stage=0' to avoid building any compilers.

So my version of this patch is more direct: it just turns off the
appropriate dependencies using a variable set by 'make 1', 'make 2',
etc.