bitbake.conf: don't set CCACHE_DIR to $HOME by default
If the user hasn't inherited ccache.bbclass then CCACHE_DIR is set to $HOME.
This was to work around a bug (#2554) for some users where if ccache < 3.1.10
(released 2014-10-19) was installed and enabled by default (i.e. /usr/bin/gcc is
a symlink to ccache) and ccache.bbclass wasn't being inherited then autogen
would fail to build because it sets $HOME to /dev/null during the build and
ccache (prior to 3.1.10) would always create CCACHE_DIR even if it was disabled.
As the default is $HOME/.ccache, this results in ccache attempting to create
/dev/null/.ccache.
However there was a mistake in this assignment of CCACHE_DIR - it should be
$HOME/.ccache - as ccache will do cleanup inside CCACHE_DIR which will result in
it deleting $HOME/tmp. In the future when we can assume that everyone has
ccache 3.1.10 onwards this assignment can be deleted, but as of now we still
support OpenSUSE 13.2 which ships with 3.1.9 so fix the assignment to be
$HOME/.ccache.
[ YOCTO #9798 ]
Signed-off-by: Ross Burton <ross.burton@intel.com>
