Sample addresses belonging to external DSOs (buildid doesn't match the current file) are treated as external (0). Buildid for the main binary is expected to be omitted. Test Plan: added pre-aggregated-perf-buildid.test Reviewers: paschalis-mpeis, maksfb, yavtuk, ayermolo, yozhu, rafaelauler, yota9 Reviewed By: paschalis-mpeis Pull Request: https://github.com/llvm/llvm-project/pull/186931