runtime: fix tv_sec handling for netbsd/386
runtime: fix tv_sec handling for netbsd/386

On netbsd/386, tv_sec is a 64-bit integer for both timeval and timespec.
Fix the time handling code so that it works correctly.

R=golang-dev, rsc, m4dh4tt3r
CC=golang-dev
http://codereview.appspot.com/6256056

pombredanne/go-deleteme,tv42/old-go,apparentlymart/golang,dsriram/golang,apparentlymart/golang,gnanderson/go,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,apparentlymart/golang,dsriram/golang,apparentlymart/golang,gnanderson/go,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,gnanderson/go,gnanderson/go,pombredanne/go-deleteme,tv42/old-go,dsriram/golang,pombredanne/go-deleteme,gnanderson/go,dsriram/golang,tv42/old-go,gnanderson/go,apparentlymart/golang,dsriram/golang,apparentlymart/golang,tv42/old-go,apparentlymart/golang,dsriram/golang,gnanderson/go,dsriram/golang,pombredanne/go-deleteme