other/42980: fix make -j install

[Ralf Wildenhues]

Hello DJ,

* DJ Delorie wrote on Mon, Mar 01, 2010 at 09:46:57PM CET:
> 
> > 0) Forbid parallel install, in documentation or in code.  Since install
> 
> I've been putting .NOTPARALLEL: in my top-level Makefile for some time
> now.

Fair enough for a release; having parallel toplevel 'make all' can be
helpful for development though, so if fixing dependency issues is
feasible, it would be better.

For issue (c) however, which I was discussing in the mail you reply to,
you'd need to disable parallel make in the multilib directories like
libmudflab, libjava etc.  A plain .NOTPARALLEL in, say, libjava, would
be quite painful for java developers, I'd guess.  Now, for those
directories allowing GNU make constructs, we can do a bit better, a la

  ifneq ($(filter %install%, $(MAKECMDGOALS)), )
  .NOTPARALLEL
  endif

but that still seems ugly.

Thanks,
Ralf