Hello. As far as I understand the situation, disabling the whole patch at https://anonscm.debian.org/viewvc/gcccvs/branches/sid/gcc-7/debian/patches/ada-default-project-path.diff?view=markup was the right choice for gnat-7. It may probably be dropped, as gprbuild is already patched to search projects in both /usr/share/gpr (upstream default) and /usr/share/ada/adainclude (Debian default).