Quick test building a module cross all targets and architectures

Hi,

We have NO_MODULES for building kernel without modules, but no NO_KERNEL 
to only build the modules.

What do you think about the following patch:

> diff --git a/sys/conf/kern.post.mk b/sys/conf/kern.post.mk
> index ddf828e..f0920df 100644
> --- a/sys/conf/kern.post.mk
> +++ b/sys/conf/kern.post.mk
> _at__at_ -32,7 +32,11 _at__at_ KERN_DEBUGDIR?=      ${DEBUGDIR}
>
>  .for target in all clean cleandepend cleandir clobber depend install \
>      obj reinstall tags
> +.if !defined(NO_KERNEL)
>  ${target}: kernel-${target}
> +.else
> +${target}:
> +.endif
>  .if !defined(MODULES_WITH_WORLD) && !defined(NO_MODULES) && exists($S/modules)
>  ${target}: modules-${target}
>  modules-${target}:

It allows only a single module with MODULES_OVERRIDE= and NO_KERNEL=YES 
to be built with universe in very little time. This can save a lot of 
build time when changes are limited to a set of kernel modules.

--HPS