Quick hack to make fast kernel builds easier [really cross-build support]

[Sam Leffler]

M. Warner Losh wrote:
> In message: <20090111191251.GA74450 at zim.MIT.EDU>
>             David Schultz <das at FreeBSD.ORG> writes:
> : On Sun, Jan 11, 2009, Ed Schouten wrote:
> : > I often just run `make' in /usr/obj/...,
> : > which also saves some typing, but unfortunately that doesn't work when
> : > cross compiling.
> : 
> : Also, as far as I know, there's no convenient way to rebuild a
> : single module for another architecture. I use the following script
> : called 'arch' to set the appropriate environment variables, so if
> : I've already run 'make universe' and I want to rebuild libc for
> : sparc64, I say:
> : 
> :    cd /usr/src/lib/libc && arch sparc64 make
> : 
> : It would be nice if there were a better mechanism for this that's
> : integrated into the build system.
>
> I do one of the following:
>
> (1) env TARGET=arm make buildworld -DNO_CLEAN
>
> or
>
> (2) env TARGET=arm make buildenv
> $ cd lib/libc && make
>
> These both work out well enough in practice for me.  I've wanted a
> target that was 'reworld' that just did an 'all' and maybe a few other
> things, but I've never had the time to polish this up (had it in a
> couple of trees that I lost due to disk failure).
>
> I do agree it would be nice if there was some way to do 'all' for a
> subdirectory with a 'trust me, I know what I'm doing, so don't do all
> that other stuff' flag.
>
>   
I told das privately but will note publicly that:

tools/tools/nanobsd/gateworks

uses make buildenv to cross-build various bits.  At some point I want to 
promote some of the shell code to be part of nanobsd but until we've got 
something to deal with ports I'm in no hurry.

    Sam