They are parsing a Makefile to determine its input and output paths, so the Makefile has to be changing for the script to yield different behavior.
<rdar://problem/115123881>
Pull request: https://github.com/WebKit/WebKit/pull/17559
Committed 267805@main (fae8124ad3b9): <https://commits.webkit.org/267805@main> Reviewed commits have been landed. Closing PR #17559 and removing active labels.