build system: Allow running make what-jenkins-does without ccache

coverity isn't too happy with ccache, and given the current setup
it also isn't too useful.

Change-Id: I420fdd7350dff29296d7101569cb183afe1f92d6
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: http://review.coreboot.org/8478
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Marc Jones <marc.jones@se-eng.com>
2 files changed