Created attachment 546908 [details] clang-9999.ebuild.patch git-r3.eclass allows the substitution of the EGIT_REPO_URI with ${PN}_LIVE_REPO, but this isn't used with clang-9999 as it has its own src_unpack The proposed patch allows the substitution selectively for all repositories.
The *_LIVE_REPO API is obsolete. Please use EGIT_OVERRIDE_* instead which supports multi-repo ebuilds. And yes, I know I need to write a better documentation for it. Maybe make it print correct variable names while fetching.