crossdirect: use native ccache, fix armhf error

(this description is outdated, I went with using native ccache instead, see the commit message)

Install ccache-cross-symlinks into the foreign arch chroot, when using crossdirect. This allows ./configure scripts to find g++ binaries with the full hostspec prefixed, like armv6-alpine-linux-muslgnueabihf-g++. Therefore this patch fixes a follow up error we've gotten from libtool:

error: unsupported hardcode properties

Fixes pmaports#223 (closed) (I'll post more details there.)