New comment by ackalker on void-packages repository

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

Comment:
Some more digging: `configure_file()` expects a path _relative to `prefix` for its `install` keyword argument, but the substitution inside the JSON files needs to be done with an _absolute_ path. 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()`.