With the recursive descent parser that gccgo uses, I think
that it doesn't make sense to try to match a statement where a
statement is not expected.  If the construct is not a
statement, you will just get bizarre error messages.

topexpr.go:9:1: error: expected declaration
topexpr.go:14:1: error: expected declaration
topexpr.go:19:1: error: expected declaration

R=rsc, r2
CC=golang-dev
https://golang.org/cl/2175041