sizeof(Adr) from 24 bytes down to 20 bytes.
sizeof(Prog) from 84 bytes down to 76 bytes.

5l linking cmd/godoc statistics:
Before:
Maximum resident set size (kbytes): 106668
After:
Maximum resident set size (kbytes):  99412

R=golang-dev, dave
CC=golang-dev
https://golang.org/cl/7100059