Unbreak the build broken by tab-bar.el changes

Unbreak the build broken by tab-bar.el changes

Without this change, compiling tab-bar.el errors out:
In tab-bar--load-buttons:
tab-bar.el:161:18: Warning: reference to free variable `tab-bar-new'
tab-bar.el:174:6: Error: `define-icon' defined after use in
(define-icon tab-bar-close nil (cons (cons 'image
(cons "tabs/close.xpm"
(cons :margin (cons tab-bar-button-margin '(:ascent center)))))
'((text " x"))) "Icon for closing the clicked tab."
:version "29.1" :help-echo "Click to close tab")
(missing `require' of a library file?)
tab-bar.el:174:18: Warning: reference to free variable `tab-bar-close'
* lisp/tab-bar.el (eval-when-compile): Require 'icons.