cmd/compilebench: report rss measurement
cmd/compilebench: report rss measurement

Change-Id: I4a0f6e75dea97413ab22f589ae2b4f36bec4b081
Reviewed-on: https://go-review.googlesource.com/c/tools/+/223750
Reviewed-by: Austin Clements <7ea35d812706d9213868749011af1ed4fa2f6aa0@google.com>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools