effectively kill depend as an independant target (there are a few corners

effectively kill depend as an independant target (there are a few corners
where a separate depend step is still needed, mostly gcc3 and mesa).

Use of BUILDFIRST is mostly enough to make sure important stuff is built
first.

Otherwise, this makes use of -M* compiler options to generate dependencies
on the fly.  There is a bit of behind-the-scene for targets with several
steps (like yacc and/or libraries) and the compiler needs extra hand-holding
with assembler files (don't know why, don't care).

Idea based on guenther@'s initial kernel work, loads of input from
drahn, aoyama, tb, etc.

okay tb@

"why wait" deraadt@