[Bug] make gitweb with GITWEB_JS set fails to build

What did you do before the bug happened? (Steps to reproduce your issue)

I ran make gitweb with the GITWEB_JS variable set on git 2.39.2, specifically:

     make gitweb GITWEB_JS=/www/gitweb.js

What did you expect to happen? (Expected behavior)

I expected the build to pass and that the GITWEB_JS (or GITWEB_CSS) variable will only be used for changing the path for gitweb.js in gitweb.cgi like it used to before 2.38.0 (before 564ebde3d323fc3b22534dcbb32723807771b955)

What happened instead? (Actual behavior)

The build failed with:

         GEN gitweb/gitweb.cgi
     make: *** No rule to make target 'gitweb//www/gitweb.js', needed by 
'gitweb'.  Stop.

What's different between what you expected and what actually happened?

Anything else you want to add:

This is caused by 564ebde3d323fc3b22534dcbb32723807771b955, but I am not sure what exactly is the issue there, so I am only reporting this and leaving the fix to someone else.

[System Info] git version: git version 2.39.2 cpu: x86_64 no commit associated with this build sizeof-long: 8 sizeof-size_t: 8 shell-path: /bin/sh compiler info: gnuc: 12.2 libc info: glibc: 2.36 $SHELL (typically, interactive shell): /bin/bash