runtime/cgo: use pthread_getattr_np on Android

runtime/cgo: use pthread_getattr_np on Android

It is defined in bionic libc since at least API level 3. Use it.

Updates #68285.

Change-Id: I215c2d61d5612e7c0298b2cb69875690f8fbea66
Reviewed-on: https://go-review.googlesource.com/c/go/+/626275
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>