runtime: fix mingw build, implement missing destroylock()
runtime: fix mingw build, implement missing destroylock()

R=golang-dev, rsc
CC=golang-dev
http://codereview.appspot.com/747041

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

tianon/debian-golang,gnanderson/go,tv42/old-go,apparentlymart/golang,tianon/debian-golang,pombredanne/go-deleteme,tianon/debian-golang,apparentlymart/golang,pombredanne/go-deleteme,dsriram/golang,ssrl/go,h8liu/golang,nightlyone/golang,ssrl/go,ssrl/go,apparentlymart/golang,tv42/old-go,gnanderson/go,tv42/old-go,tianon/debian-golang,pombredanne/go-deleteme,bdwalton/debian-golang,bdwalton/debian-golang,dsriram/golang,nightlyone/golang,tv42/old-go,tv42/old-go,h8liu/golang,h8liu/golang,pombredanne/go-deleteme,h8liu/golang,dsriram/golang,gnanderson/go,gnanderson/go,apparentlymart/golang,h8liu/golang,pombredanne/go-deleteme,apparentlymart/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,nightlyone/golang,tv42/old-go,ssrl/go,bdwalton/debian-golang,tianon/debian-golang,tianon/debian-golang,apparentlymart/golang,tianon/debian-golang,bdwalton/debian-golang,nightlyone/golang,tv42/old-go,nightlyone/golang,h8liu/golang,dsriram/golang,ssrl/go,dsriram/golang,dsriram/golang,apparentlymart/golang,gnanderson/go,dsriram/golang,bdwalton/debian-golang,bdwalton/debian-golang,nightlyone/golang,ssrl/go,nightlyone/golang,bdwalton/debian-golang,tianon/debian-golang,ssrl/go,bdwalton/debian-golang,gnanderson/go,h8liu/golang,gnanderson/go