[A-A-P-develop] Handling build attributes

[Adriaan de G. <ad...@cs...>]

Suppose (this is a hypothetical recipe - I know objecttype doesn't make much 
sense in the places where I use it here):

:program a : { add_INCLUDE=-Ithing } 
	{ objecttype = frobnicated } 
	b.c 
	c.c { objecttype = discombobulate } { add_INCLUDE = -Iboo } 
	d.c { var_INCLUDE=-I/usr }

I had an earlier patch that applied build attributes ( { add_INCLUDE=-Ithing } 
{ objecttype = frobnicated } ) to sources, but it did it wrong and Bram told 
me to use spaces around = and to put the attributes in the build_attr, not in 
the nodes. So I have, and patch is attached. It's somewhat larger than 
before, because it takes the following into account:

- If a source sets an attribute that is also a build attribute, then the 
source attribute takes precedence. So c.c is compiled to a discombobulated 
object file, and not a frobnicated one. 

- If a source has an var_* attribute and the build attributes have a 
corresponding var_* or add_*, the source takes precedence.

- If a source has an add_ attribute and the build has a var_ attribute, 
compute var_ + add_ and set that as var_

- If a source has an add_ attribute and build has one too, prepend the build 
attribute to the source attribute.

This recipe shows all the combinations:

:program b : { var_INCLUDE = -I1 } { add_CFLAGS = -DD=2 }
        b.c
        c.c { add_INCLUDE = -I/usr/local/include }
        d.c { var_INCLUDE = -I/root }
        e.c { add_CFLAGS = -DDEBUG }
        f.c { var_CFLAGS = -DFROBNICATE }

with AAP output:

Aap:  cc   -I1 -DD=2   -MM b.c > build-FreeBSD4_9_RC/b.c.aap
Aap: cc   -I1 -O2 -DD=2 -DD=2 -c -o build-FreeBSD4_9_RC/b.o b.c
Aap:  cc   -I1 -I/usr/local/include -DD=2   -MM c.c > 
build-FreeBSD4_9_RC/c.c.aap
Aap: cc   -I1 -I/usr/local/include -O2 -DD=2 -DD=2 -c -o 
build-FreeBSD4_9_RC/c.o c.c
Aap:  cc   -I/root -DD=2   -MM d.c > build-FreeBSD4_9_RC/d.c.aap
Aap: cc   -I/root -O2 -DD=2 -DD=2 -c -o build-FreeBSD4_9_RC/d.o d.c
Aap:  cc   -I1 -DD=2 -DDEBUG   -MM e.c > build-FreeBSD4_9_RC/e.c.aap
Aap: cc   -I1 -O2 -DD=2 -DDEBUG -DD=2 -DDEBUG -c -o build-FreeBSD4_9_RC/e.o 
e.c
Aap:  cc   -I1 -DFROBNICATE   -MM f.c > build-FreeBSD4_9_RC/f.c.aap
Aap: cc   -I1 -O2 -DFROBNICATE -c -o build-FreeBSD4_9_RC/f.o f.c

Heck, it makes sense to me. Docs are forthcoming, unless thinking about bdir() 
gets in the way.