icecc-create-env: Symlink alternate names

Instead of renaming files to a new path in the toolchain archive, keep
the files with their original paths and create a relative symbolic link
from the new path to the original file.

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>