Upgrading 8.2 to 9.0-rc2: missing directories at 'make installkernel'

When upgrading a FreeBSD 8.2 (amd64) to today's csup (tag=RELENG_9,
i.e. 9.0-RC2), the standard procedure got itself into trouble:

  rm -rf /usr/obj
  make buildworld
  make buildkernel KERNCONF=xxx
  make installkernel KERNCONF=xxx

(the xxx is mostly a plain vanilla 'include GENERIC'
with pf altq and GEOM_ELI added).

The 'make installkernel' phase was failing on missing directories.
Creating these manually and repeating the make installkernel
eventually lead to a successful installation.

The missing directories that needed to be created manually were:

  /usr/include/clang  (and possibly /usr/include/clang/3.0 )
  /usr/include/gcc    (and possibly /usr/include/gcc/4.2 )
  /libexec/resolvconf
  /usr/share/doc/llvm
  /usr/share/locale/la_LN.ISO8859-13/LC_COLLATE [...]

Actually the /usr/share/locale was a mess, missing several
files, so I ended up replacing this directory by what has been
built in the 'make buildworld' phase under /usr/obj.

Just wanted to point out a possible problem others may encounter.

  Mark