This is the same retry loop we use in _cgo_try_pthread_create in runtime/cgo.

Fixes #25078

Change-Id: I7ef4d4fc7fb89cbfb674c4f93cbdd7a033dd8983
Reviewed-on: https://go-review.googlesource.com/121096
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>