bitbake.conf: mark all directories as safe for git to read

bitbake.conf: mark all directories as safe for git to read

Recent git releases containing [1] have an ownership check when opening
repositories, and refuse to open a repository if it is owned by a
different user.

This breaks any use of git in do_install, as that is executed by the
(fake) root user. Whilst not common, this does happen.

Setting the git configuration safe.directories=* disables this check, so
that git is usable in fakeroot tasks.  This can be set globally via the
internal environment variable GIT_CONFIG_PARAMETERS, we can't use
GIT_CONFIG_*_KEY/VALUE as that isn't present in all the releases which
have the ownership check.

We already set GIT_CEILING_DIRECTORIES to ensure that git doesn't
recurse up out of the work directory, so this isn't a security issue.

[1] https://github.com/git/git/commit/8959555cee7ec045958f9b6dd62e541affb7e7d9

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>