proposal: merge waf build of s4 to master

[tridge at samba.org]

Hi Simo,

 > But in general a qemu dependency seem quite a lot to ask when autotools
 > do not require anything just that you pass correct cached ac_cv_ vars.

yes, while I think using --cross-execute is ideal if its available, I
agree we need a method for when its too difficult or not possible. See
my last msg for a proposed solution:

  http://lists.samba.org/archive/samba-technical/2010-April/070563.html

I haven't actually ever used the cached ac_cv_* method with autoconf
for cross-compilation. I don't think I'll try and implement it in a
autotools compatible way though. I think cross-compiling is
specialised enough that requiring people to read some docs on
wiki.samba.org to understand how to do it with our build system isn't
unreasonable.

I think implementing the above proposal would be quite easy. I'll
probably also make it that you can do both steps at once, using:

 waf configure --cross-answers=myanswers.txt --cross-answers-build=myanswers.txt

it would then add any new template entries to myanswers.txt, and would
using any existing ones that are there. You will know you are done
when there are no UNKNOWN entries in the file.

It would be an iterative process, as a configure test answer can
change what the remaining configure tests are.

I may also make the file be a valid python data structure (maybe in
cPickle format?). That would allow the answer to be multi-line, in
case someone has a configure test that returns a complex string. We
don't have any of those at the moment, but there is nothing stopping
someone adding one.

If you like the general approach, I think (hope!) implementing this
will be fairly simple.

Cheers, Tridge