phase2: sanitize SDK host command symlinks

phase2: sanitize SDK host command symlinks

The SDK archive might contain symlinks like

  staging_dir/host/bin/gcc -> /builder/arc770_generic/ccache_cc.sh

which may result in host compile failures when a slave has been used
for both phase1 and phase2 builds.

Add a new step which purges such links when running the SDK until
buildroot is eventually fixed to not put suhc links into the archive
in the first place.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>