runtime: fix VDSO lookup to use dynamic hash table

Reportedly in the Linux 3.16 kernel the VDSO will not have
section headers or a normal symbol table.

Too late for 1.3 but perhaps for 1.3.1, if there is one.

Fixes issue 8197.

LGTM=rsc
R=golang-codereviews, mattn.jp, rsc
CC=golang-codereviews
https://codereview.appspot.com/101260044
A+C: Alan Shreve (individual CLA)

Generated by addca.

R=gobot
CC=golang-codereviews
https://codereview.appspot.com/102410044
syscall: implement syscall.Getppid() on Windows

Also added a test to verify os.Getppid() works across all platforms

LGTM=alex.brainman
R=golang-codereviews, alex.brainman, shreveal, iant
CC=golang-codereviews
https://codereview.appspot.com/102320044

Committer: Alex Brainman <alex.brainman@gmail.com>
os: disable TestGetppid on plan9

Fixes build.

LGTM=dave
R=golang-codereviews, dave
CC=golang-codereviews
https://codereview.appspot.com/105140047