Homogenize reachover build file structure with that of kyua-cli:

- Move the majority of the common build definitions to the top-level
Makefile.inc and ensure this gets included everywhere.
- Move the bconfig.h file to the top-level directory.
- Add a statically-generated defs.h file instead of creating one
during the build. Easier to understand and less chances for things
to go wrong.
- Make sure all files using ATF_VERSION have the right dependency to
trigger a rebuild when the value changes.
- Clean up stale -I flags.

This is all mostly for simplicity reasons and to reduce the cognitive
load required to understand the build of the atf and kyua-* packages.

I have tested this with both MKKYUA=no/yes and non-clean/clean builds
so hopefully I got the details right. But if not, let me know please.

Adjust reachover Makefiles for atf-0.19.

The main change here is that the atf-config, atf-report, atf-run and
atf-version tools no longer depend on libatf-c nor libatf-c++. Instead,
they depend on an internal libtools.a that contains code specifically
for these tools and nothing else, making them self-contained.

branches: 1.3.6; 1.3.12;
Adjust reachover makefiles for atf 0.9.

Wrap these with .if ${MKSHARE} != "no"

Add reachover Makefiles to build ATF 0.6. These replace the old Makefiles
that were spread all around the tree when ATF lived in dist/atf.

Rebase to HEAD as of a few days ago.

sync with head.

for a reference, the tree before this commit was tagged
as yamt-pagecache-tag8.

this commit was splitted into small chunks to avoid
a limitation of cvs. ("Protocol error: too many arguments")