Typically generated files are not checked in git, but there could be exceptions. This file is not installed in lib/pkgconfig so it cannot be seen by any other module.
It's not a big issue, but it will hinder some work in the future because it is the only .pc file in git in X.Org . I am including a patch to remove it, if it is the right course of action. Feel free to keep it if it has some purpose that isn't obvious.
I noticed Debian distro removed it:
Created attachment 29343 [details] [review]
[PATCH] Remove unused generated libcomp.pc #23801
No, this file dates from the very early days of pixman, where I considered calling it libcomp. It has not ever served a purpose.
Fixed in fefe2a5d24591846281bb9bf0e85d42822e1716e.