cmd/gc: racewalk: collect stack traces in sync and sync/atomic W/o this change stack traces do not show from where sync.Once() or atomic.XXX was called. This change add funcenter/exit instrumentation to sync/sync.atomic packages.
cmd/gc: racewalk: collect stack traces in sync and sync/atomic
W/o this change stack traces do not show from where sync.Once()
or atomic.XXX was called.
This change add funcenter/exit instrumentation to sync/sync.atomic
packages.

R=golang-dev
CC=golang-dev
https://codereview.appspot.com/6854112

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