cgocall.c: define the CBARGS macro for GOARCH_amd64p32. I don't think the value of this macro will ever be used under nacl/amd64p32 but it is required to compile even if cgo is not used.

hashmap.goc: amd64p32 uses 32bit words.

LGTM=iant
R=rsc, iant
CC=golang-codereviews
https://golang.org/cl/69960044