sync/atomic: skip broken tests on freebsd/arm and netbsd/arm
sync/atomic: skip broken tests on freebsd/arm and netbsd/arm

Update issue 7338

The nil deref tests are currently failing on the *bsd/arm platforms. In an effort to avoid the build deteriorating further I would like to skip these tests on freebsd/arm and netbsd/arm.

LGTM=bradfitz, minux.ma
R=golang-codereviews, bradfitz, minux.ma
CC=golang-codereviews
https://codereview.appspot.com/69870045

pombredanne/go-deleteme,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go