Always build kernel with linaro
Update core makefiles
Always rebuild build.prop file

build.prop file was not rebuilt after changes to $(PRODUCT_PROPERTY_OVERRIDES)
Without this patch, if change I681fd92e will be merged,
the wrong date will be always in the zip file's name
(date of building build.prop and not the current date).
This patch simply forces rebuilding build.prop every time.

Change-Id: I5071072cdbb34865e32403a2e7ce0f705ff9daee
Revert "userdebug -> eng"

This reverts commit 2ecb6309df326c03b75304ea3f66b97ea94dcbf0.
Allow host ccache
Use CCACHE_COMPRESS
Allow host ccache for kernel too