Could be a clash with another file including `stdbool.h` or also defining own `bool` type.
IMO, it should either include `stdbool.h` and use the standard `bool` (alias of `_Bool`) or else use `gboolean` that is already available via the `glib.h` include.
@rezso if you want to test, try removing the offending line (55) and putting `#include <stdbool.h>` on line 32.