Gentoo's Bugzilla –
Attachment 371430 Details for
Bug 503046dev-libs/protobuf-2.5.0 on PPC - In file included from google/protobuf/stubs/atomicops_internals_x86_gcc.cc:36: ./google/protobuf/stubs/platform_macros.h:61:2: error: #error Host architecture was not detected as supported by protobuf