It is just far too slow.
I have a CL for Go 1.6 that makes many of these into internal tests.
That will improve the coverage.

It does not matter much, because basically none of the go command
tests are architecture dependent, so the other builders will catch
any problems.

Fixes freebsd-arm builder.

Change-Id: I8b2f6ac2cc1e7657019f7731c6662dc43e20bfb5
Reviewed-on: https://go-review.googlesource.com/13166Reviewed-by: Ian Lance Taylor <iant@golang.org>