unbreak individual module building

[Matthew Dillon]

:Sorry, I didn't read the commit log carefully enough :-P.  Thanks for
:the explaination.
:
:>    Because of all this the buildworld (in src/include/Makefile*) and
:>    buildkernel (in src/Makefile.inc1) targets synthesize the 'missing'
:>    <machine/*.h> header files by either creating a forwarding header
:>    file to <cpu/*.h> or simply copying the <cpu/*.h> to the machine/
:>    sub directory in the object tree or in /usr/include.
:
:I prefer to synthesizing missing headers:
:http://leaf.dragonflybsd.org/~sephe/config2.diff
:
:Please review it.
:
:Best Regards,
:sephe

    This will generate a copy for each module, but I think that might be ok
    since modules are not usually built without a kernel context.  I presume
    that the only time this mechanism is used is when you build a module
    manually, right?

						-Matt