cmd/compile: textual and binary importer ignore //go:nointerface pragma

[griesemer]

This bug was introduced by https://go-review.googlesource.com/19966 (parser.go):

In https://go-review.googlesource.com/#/c/19966/3/src/cmd/compile/internal/gc/parser.go, line 2061 on the left still respects nointerface, while the new line 2057 simply sets it to false. As a result, the further translation to the binary format doesn't know about it either.

This is a regression and needs to be fixed for 1.7.

cc: @ianlancetaylor

[gopherbot]

CL https://golang.org/cl/24648 mentions this issue.