go/ssa: report memory consumption separated by phase in stdlib_test
go/ssa: report memory consumption separated by phase in stdlib_test

LGTM=gri
R=gri
CC=golang-codereviews
https://codereview.appspot.com/170600043

karmakaze/go.tools,karmakaze/go.tools,karmakaze/go.tools,karmakaze/go.tools,karmakaze/go.tools