We might want to replace some linker's feature by debug/macho in future.
This CL gathers information of required constants.

Change-Id: Iea14abdb32709a4f5404a17874f9c925d29ba999
Reviewed-on: https://go-review.googlesource.com/55252Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>