New comment by ackalker on void-packages repository

https://github.com/void-linux/void-packages/issues/27965#issuecomment-766400380

Comment:
Some more digging: the [documentation for `configure_file()`](https://mesonbuild.com/Reference-manual.html#configure_file) states that its `install_dir` keyword argument expects a subdirectory, i.e. a path _relative_ to, the value of `prefix`, but the `configuration` keyword argument which supplies the rule for the substitution of `@DATADIR@` inside the JSON files needs to be given an _absolute_ path for the files to be usable. Because `datadir` is not configured, it defaults to `share` which is a relative path. `qemu_datadir` is derived from the value of `datadir`, so it becomes a relative path as well, and so both `configuration` and `install_dir` end up using relative paths as well.

The way things are curently setup in Qemu's build system, setting `datadir` to an absolute path would also make `qemu_datadir` absolute, but I don't know if this violates the requirements for `configure_file()`.