Something is really wrong. Look at this transcript:

rpg@rpg-mbp-2: ~/lisp/asdf $ git checkout 3.3.4
Note: switching to '3.3.4'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by switching back to a branch.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -c with the switch command. Example:

  git switch -c <new-branch-name>

Or undo this operation with:

  git switch -

Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at 082f4ed4 Bump version to 3.3.4
rpg@rpg-mbp-2: ~/lisp/asdf $ find . -name '*.lisp' -exec fgrep -iq SYSTEM-INPUT-FILES {} \; -print
rpg@rpg-mbp-2: ~/lisp/asdf $

Similarly, after loading 3.3.4 into SBCL, I see this:

CL-USER(1): (apropos '#:system-input-files)

CL-USER(2):

Similarly on Lispworks:
```
CL-USER 3 > (load "/Users/rpg/lisp/asdf/build/asdf.lisp")
; Loading text file /Users/rpg/lisp/asdf/build/asdf.lisp

P"/Users/rpg/lisp/asdf/build/asdf.lisp"

CL-USER 4 > (apropos '#:system-input-files)

CL-USER 5 >
```

I just tried (require :asdf) on Lispworks, and still no system-input-files.

I simply have no idea where this is coming from. Please send a minimum working example for Lispworks.