README file
Move the list of kernel headers so we can use it in multiple places

We want to be able to install, or uninstall, these headers for
different packages.
Various overhauls to support more build options

* Add GCONV_PATH to the exported SDK environment script.
* Try to get $PYTHONHOME set correctly so gdb with python support
  can report its version more reliably.
* Downgrade some toolchain version issues to warnings.
* Make more CSL_VER_* variables get set only if they are not already
  set, allowing user overrides to bypass version computations.
* More fixups for the PNBLACKLIST set.
* Rework tcmode files to provide options in a more orthogonal way,
  using new TCMODE_EXTRA.
* Provide a default (possibly wrong) for CSL_TARGET_CORE.
* More PREFERRED_PROVIDER settings.
* Fancy magic to install the 32-bit binaries on x86-64 targets as
  a target toolchain.
* Allow override of TOOLCHAIN_SHARED_BINDIR in some cases.
* Bump LAYERVERSION_sourcery.
* Specify dependency on "core".
* If ldconfig isn't being installed, remove it so we don't get warnings.
* Set various PKG_* values automatically.
* Automatically install kernel headers when installing libc-dev.
* Add getconf/.debug to -dbg package.
* Add EXTERNAL_SOURCERY_EXTRA_SYSROOT_FILES magic to support special
  files in unexpected locations, such as /lib/ld-linux-aarch64.so.1 for
  a multilib where absolutely everything else is in /lib64.
* Move some files (e.g., nscd, iconvconfig, zdump) from ${bindir} to
  ${base_sbindir}.
* Remove a number of unused/unpackaged files.
* Drop some tools (mklibs, prelink) from the installed SDK. Partially
  because they aren't useful there, partially because there were huge
  difficulties trying to get them to work.
* Copy in Python parts for gdb, but make them optional because not
  all CS toolchains have gdb.
* A couple of indentation fixups.
* Add libgcov and libssp packaging.
* Ensure C++ headers get included.
* Allow for a fixed/prebuilt kernel header tarball.
* Move symlink creation into recipes (see below).
* Drop a system_glibc hack that was specific to a feature we no longer used.
* Update list of likely kernel header directories.
* New sourcery-tc.bb recipe installs toolchain on target. May be
  too vendor-specific still.
* Toolchain wrappers bbappend which is only relevant if you have the
  toolchain wrappers. (Not sure whether the wrappers should perhaps also
  get added to this layer.)

Symlink creation turns out to be harder than it looked. In the previous
version, symlink creation was handled at startup time, then run once for
each multilib. Unfortunately, this produces the wrong names, and it's
basically impossible to correctly compute the triplet name that will be
used for a multilib outside of additional transformations which occur only
when processing a specific recipe. Thus, while we could determine that there
was an "i586" multilib, we would guess the name "i586-wrs-linux", but the
actual name was "i586-wrsmllib32-linux". Whoops. So that gets moved into
a hunk of code which can be used in per-multilib packaging, and run early
enough to make the symlinks show up in time. This has the side effect
of meaning that the symlink creation doesn't get re-run during startup. Yay.