kmk/kBuild: rename footer.kmk output variables like $(target)_OBJS_

[bird]

The variables set by footer.kmk in pass two will be named $(target)_2_BLAH. The ones set by footer.kmk in pass 1 will be named $(target)_1_BLAH. The variables set by subfooter.kmk and subheader.kmk will be named $(target)_0_BLAH. This will help avoiding confusion wrt to when they are safe to use and when second expansion is required.

Other variables:

• $(target)_OUTPUT_
• $(target)_OUTPUT_MAYBE_
• $(target)_DEPEND_
• $(target)_DEPORD_

Already official ones that may be considered for renaming to the new scheme:

• PATH_$(target)
• INSTARGET_$(target)
• TARGET_$(target)

The old values that are *known* to be in use will kick around until 0.3.0, starting with 0.2.1 kBuild will bitch about them.

[bird]

(In [2020]) kbuild.c: $(target)_OBJS_ -> $(target)_2_OBJS. References #57.

[bird]

(In [2239]) footer.kmk,subheader.kmk,subfooter.kmk,qt3.kmk,qt4.kmk: PATH_$(target) -> $(target)_0_OUTDIR, old variable is still valid for a while. References #57.

[bird]

See also [2234], [2236], [2237], [2238], [2240], [2241].

Summary:

  - PATH_$(target)          -> $(target)_0_OUTDIR
  - TARGET_$(target)        -> $(target)_1_TARGET
  - $(target)_OUTPUT_       -> $(target)_2_OUTPUT
  - $(target)_OUTPUT_MAYBE_ -> $(target)_2_OUTPUT_MAYBE
  - $(target)_DEPEND_       -> $(target)_2_DEPEND
  - $(target)_DEPORD_       -> $(target)_2_DEPORD

The $(target)_$(source) variants of the above has been hidden, the same has $(target)_CMDS. For FETCH targets there are some infix variants of the some of these variables, these have received the same general treatment.

INSTARGET_$(target) is left for the installation reworking.