Ubuntu 18.04 (gi 1.56.1) and Debian Buster (1.58.3) do not have the sources-top-dirs parameter available in g-ir-scanner. (Added in 1.59.1) Patch incoming
Created attachment 417874 [details] Patch
Committed r271608: <https://trac.webkit.org/changeset/271608> All reviewed patches have been landed. Closing bug and clearing flags on attachment 417874 [details].
Oops, sorry. :(