This test triggers a large number of usleep(100)s. linux/arm, openbsd,
and solaris have very poor timer resolution on the builders, so
usleep(100) actually gives up the whole scheduling quantum. On Linux
and OpenBSD (and probably Solaris), profiling signals are only
generated when a process completes a whole scheduling quantum, so this
test often gets zero profiling signals and fails.

Until we figure out what to do about this, skip this test on these
platforms.

Updates #13405.

Change-Id: Ica94e4a8ae7a8df3e5a840504f83ee2ec08727df
Reviewed-on: https://go-review.googlesource.com/18252Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Austin Clements <austin@google.com>