Re: rust: NetBSD 9 earmv7, version selection, RUST_TYPE

[Greg Troxel <gdt%lexort.com@localhost>]

I think we're converged, so I have committed a version that addresses
all the comments received:

  Uses RUST_TYPE?= so a user's declaration for src should be respected.

  Tests NATIVE_MACHINE_PLATFORM so that cross from x86_64 to earm should
  still use source.  And as a bonus, crossbuilding for NetBSD/amd64 from
  earm should use binary!

  Notes that likely other arches need to be included (but declines to
  guess).


I don't know if rust176 should be pruned or not; I don't see that anyone
would want to use it.