go.tools/go/types: use WordSize as function pointer size
go.tools/go/types: use WordSize as function pointer size

Both gc and gccgo appear to use this size, so it seems appropriate
to use it here.

R=gri
CC=golang-codereviews, golang-dev, iant, rsc
https://codereview.appspot.com/52290043

Committer: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

chenjianlong/go.tools,karmakaze/go.tools,lattera/go.tools,lattera/go.tools,chenjianlong/go.tools,karmakaze/go.tools,karmakaze/go.tools,chenjianlong/go.tools,karmakaze/go.tools,lattera/go.tools,karmakaze/go.tools