[Toybox] Out of tree build support

[Rob Landley]

On 12/18/2017 05:41 PM, Rob Landley wrote:
> (Probably configure should have VALUE?="blah" and then a shell wrapper
> that parses and sets that syntax.)

Except when I sat down to try to implement that (again) I hit the
problem that configure variable defautls reference other config
variables (such as CROSS_COMPILE="$CROSS") and even writing a simple
parser to find ?= lines and turn them into = lines, to import that as
makefile syntax it has to be CROSS_COMPILE="$(CROSS)" with gratuitous
parentheses, and that a giant rathole.

Having variables you can set in both shell and makefile contexts turns
out to be kind of annoying. What I need to do is remove all the
remaining logic from the makefile and put it in the script and have the
makefile be just a dumb wrapper around the scripts like it was intended
to be...

Rob