kexecboot: fix build when S != B

* temporarily inherit autotools-brokensep
* proper fix sent upstream

Signed-off-by: Andrea Adami <andrea.adami@gmail.com>
klcc_cross: move in target sysroot as crossscript

Klcc-cross is properly a crosscript so avoid to inherit cross.bbclass and stage
it in target sysroot under usr/bin/crossscripts.
Minor adjustment is necessary for INSTALLDIR.

Finally some magic mangling is applied fixing the paths of sstate so that it is
invalidated in case of subsequent builds targeting machines with the same
arch and in case of builds sharing the sstate cache.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Andrea Adami <andrea.adami@gmail.com>