the protobuf3.patch just adds a protobuf-3-specific include, which breaks builds when =protobuf-2* is installed. The include should be wrapped into a version check, something like #if GOOGLE_PROTOBUF_VERSION >= 3000000 #include blah... #endif
commit 295de3a6c62704f437339af9c5e3751bfa65f601 Author: Alexis Ballier <aballier@gentoo.org> Date: Sat Apr 30 17:20:39 2016 +0200 net-libs/ignition-transport: add version guards to the protobuf3 patch so that protobuf2 support still works. Bug #581214 by Victor Mataré. thanks!