sbcl: Fix failing install HEAD due to no version

The make script in sbcl gets a version string from either a
file named version.lisp-expr or a release tag in the git repo.
HEAD has neither so requires a step to create the file
with a dummy version string before the make script is run.

This commit creates that file when installing from HEAD.

Closes #26880.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>