…as cmd/compile

Other binary formats to follow.

Using our own note instead of the GNU build ID note because
we are not the GNU project, and I can't guarantee that the semantics
of our note and the semantics of the GNU note will match forever.
(Also they don't match today.)

For #11048.

Change-Id: Iec7e5a2e49d52b6d3a51b0aface2de7c77a45491
Reviewed-on: https://go-review.googlesource.com/10706
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Other binary formats to follow.

For #11048.

Change-Id: Ia2d8b47c99c99d171c014b7cfd23c1c7ada5231c
Reviewed-on: https://go-review.googlesource.com/10707
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Non-ELF binary formats are much less flexible and typically do not
have a good place to store the build ID.

We store it as raw bytes at the beginning of the text segment.

The only system I know of that will be upset about this is NaCl,
and NaCl is an ELF system and does not use this.

For #11048.

Change-Id: Iaa7ace703c4cf36392e752eea9b55e2ce49e9826
Reviewed-on: https://go-review.googlesource.com/10708
Reviewed-by: Ian Lance Taylor <iant@golang.org>