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 rules for the substitutions inside the JSON files needs to be given an _absolute_ path for it to work. This can never be accomplished by using the same value (of `qemu_datadir`) for both.
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()`.