cmd/gc: fix race compilation failure 'non-orig name'

cmd/gc: fix race compilation failure 'non-orig name'

CL 51010045 fixed the first one of these:

        cmd/gc: return canonical Node* from temp

        For historical reasons, temp was returning a copy
        of the created Node*, not the original Node*.
        This meant that if analysis recorded information in the
        returned node (for example, n->addrtaken = 1), the
        analysis would not show up on the original Node*, the
        one kept in fn->dcl and consulted during liveness
        bitmap creation.

        Correct this, and watch for it when setting addrtaken.

        Fixes #7083.

        R=khr, dave, minux.ma
        CC=golang-codereviews
        https://golang.org/cl/51010045

CL 53200043 fixed the second:

        cmd/gc: fix race build

        Missed this case in CL 51010045.

        TBR=khr
        CC=golang-codereviews
        https://golang.org/cl/53200043

This CL fixes the third. There are only three nod(OXXX, ...)
calls in sinit.c, so maybe we're done. Embarassing that it
took three CLs to find all three.

Fixes #8028.

LGTM=khr
R=golang-codereviews, khr
CC=golang-codereviews, iant
https://golang.org/cl/100800046