up-to-date: kernel 3.2.54. (Always read current kernel sources!) This topic has maintainer ["rfree"]
BuildId is the --build-id option for compiler/linker that result in unique Build ID number being added to the resulting binary like ["vmlinux"] into it's ["vmlinux/asm-notes"] section.
To get rid of it e.g. to produce SameKernel builds, edit the main Makefile and change --build-id to =none, as done by the Mempo script in https://github.com/mempo/deterministic-kernel the important part is
sed -i Makefile -e 's/--build-id/--build-id=none/g'
targeting the top-level Makefile (seems to work on amd64 builds on debian).
Perhaps certain architectures already remove this --build-id, or remove it along with removing entire .notes section, see vmlinux/asm-notes