Add scan-build support to the build system.

Add scan-build support to the build system.
When configured in Kconfig, just running "make"
calls scan-build as appropriate (however, it does not
check for the presence of scan-build)

The target directory for the scan-build report is configurable
and defaults to the scan-build default of /tmp/scan-build-$date-$num

abuild is adapted to properly run scanbuild when ran
with the -sb option.

Signed-off-by: Patrick Georgi <patrick.georgi@coresystems.de>
Acked-by: Stefan Reinauer <stepan@coresystems.de>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@5208 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1