patch: don't use pidfd on Android

[bradfitz]

Summary: don't use the pidfd system calls on Android
Upstream status: in progress; see golang#69065
Importance: critical for Android
Example prior commit: 8e2c1cf

Tailscale bug: tailscale/tailscale#13452

[bradfitz]

This problem is back. See tailscale/tailscale#13452 (comment)

I think we'll want to carry this patch going forward. We thought it was fixed upstream in Go 1.24 but it's not.

/cc @kari-ts

[bradfitz]

Go 1.24 version was #125