New review comment by oreo639 on void-packages repository

https://github.com/void-linux/void-packages/pull/48982#discussion_r1506753796

Comment:
This doesn't explain why the patch is necessary. (e.g. why can the pkg-config variables not be used? What goes wrong if they are? Why does this not affect other distros?)

A proper description would be smth like this:
```
Avoid using pkg-config variables for girdir_for_pc_file and typelibdir_for_pc_file since they include pc_sysrootdir, which cannot be overridden using `pkgconfig_define`.
meson needs non-absolute paths in order to correctly generate `datadir`.
```