patch: runtime: use uname version check for 64-bit time on 32-bit arch codepaths

[bradfitz]

We want this in Tailscale's 1.26 tree earlier:

runtime: use uname version check for 64-bit time on 32-bit arch codepaths
https://go-review.googlesource.com/c/go/+/758902/2

(for the 32-bit Synology fixes)

/cc @nickkhyl @nickoneill

[bradfitz]

Sent #163