runtime: enable sigPerThreadSyscall handling on android

runtime: enable sigPerThreadSyscall handling on android

CL 383434 forgot to enable these paths for android, which is still linux
just not via GOOS.

Fixes #51213.

Change-Id: I102e53e8671403ded6edb4ba04789154d7a0730b
Reviewed-on: https://go-review.googlesource.com/c/go/+/385954
Trust: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Austin Clements <austin@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>