broke too many assumptions makde by other parts of the source tree,
and the strategy and how it was supposed to work was never discussed
on tech-userlevel, nor was it applied consistently (to all ARM ports
and to other ports which have common MACHINE_ARCH code, such as MIPS,
m68k, powerpc).
Verified to complete a full "make build" on cats, dnard, evbarm,
and netwinder.
This is necessary to make the libstdc++ install work with the old toolchain,
since it installs <machine/_G_config.h> into /usr/src/${MACHINE}. There may
be other dependencies on the Old Way, too.
as with user-land programs, include files are installed by each directory
in the tree that has includes to install. (This allows more flexibility
as to what gets installed, makes 'partial installs' easier, and gives us
more options as to which machines' includes get installed at any given
time.) The old SYS_INCLUDES={symlinks,copies} behaviours are _both_
still supported, though at least one bug in the 'symlinks' case is
fixed by this change. Include files can't be build before installation,
so directories that have includes as targets (e.g. dev/pci) have to move
those targets into a different Makefile.