runtime: closures, defer bug fix for Native Client

misc/nacl/naclrun

src/all-nacl.bash

src/cmd/8g/ggen.c

src/cmd/8l/asm.c

src/cmd/8l/l.h

src/cmd/8l/obj.c

src/cmd/8l/span.c

src/cmd/gotest/gotest

src/pkg/Makefile

src/pkg/os/stat_nacl.go

src/pkg/runtime/Makefile

src/pkg/runtime/malloc.h

src/pkg/runtime/mgc0.c

src/pkg/runtime/nacl/386/closure.c

src/pkg/runtime/nacl/386/sys.s

src/pkg/runtime/nacl/thread.c

src/pkg/syscall/syscall_nacl.go

test/env.go

test/fixedbugs/bug243.go

test/nacl-pass.txt