Some systems, like Ubuntu, pass --build-id when linking.  The
effect is to put a note in the output file.  This is not
useful when generating an object file with the -r option, as
it eventually causes multiple build ID notes in the final
executable, all but one of which are for tiny portions of the
file and are therefore useless.

Disable that by passing an explicit --build-id=none when
linking with -r on systems that might do this.

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/119460043