cmd/dist: execute misc/cgo/testso{,var} as regular tests, not host tests
These tests use runtime.GOOS and runtime.GOARCH to determine whether
to run, so must be built and run using the destination's — not the
host's — GOOS and GOARCH.
Updates #30228
Change-Id: I6774dacd01c68b395fca8ca61f70d5879270af8a
Reviewed-on: https://go-review.googlesource.com/c/164117
Run-TryBot: Bryan C. Mills <bcmills@google.com> Reviewed-by: Jay Conrod <jayconrod@google.com>