The bootstrap restriction is to avoid needing cgo for package net.
There's no problem with building debug/elf and debug/dwarf,
so do that.

An upcoming CL is going to add more note processing code,
and it simplifies things not to have to think about the code being
missing half the time.

Change-Id: I0e2f120ac23f14db6ecfcec7bfe254a69abcf7b6
Reviewed-on: https://go-review.googlesource.com/10703Reviewed-by: Ian Lance Taylor <iant@golang.org>