cmd/5g, cmd/6g, cmd/8g, cmd/9g: zero more in componentgen

Fix a flipped nil check.
The flipped check prevented componentgen
from zeroing a non-cadable nl.
This fix reduces the number of non-SB LEAQs
in godoc from 35323 to 34920 (-1.1%).

Update #1914

Change-Id: I15ea303068835f606f883ddf4a2bb4cb2287e9ae
Reviewed-on: https://go-review.googlesource.com/2605
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>

src/cmd/5g/cgen.c

@@ -1680,7 +1680,7 @@ componentgen(Node *nr, Node *nl)
 
 	nodl = *nl;
 	if(!cadable(nl)) {
-		if(nr == N || !cadable(nr))
+		if(nr != N && !cadable(nr))
 			goto no;
 		igen(nl, &nodl, N);
 		freel = 1;

src/cmd/6g/cgen.c

@@ -1587,7 +1587,7 @@ componentgen(Node *nr, Node *nl)
 
 	nodl = *nl;
 	if(!cadable(nl)) {
-		if(nr == N || !cadable(nr))
+		if(nr != N && !cadable(nr))
 			goto no;
 		igen(nl, &nodl, N);
 		freel = 1;

src/cmd/8g/cgen.c

@@ -1427,7 +1427,7 @@ componentgen(Node *nr, Node *nl)
 
 	nodl = *nl;
 	if(!cadable(nl)) {
-		if(nr == N || !cadable(nr))
+		if(nr != N && !cadable(nr))
 			goto no;
 		igen(nl, &nodl, N);
 		freel = 1;

src/cmd/9g/cgen.c

@@ -1602,7 +1602,7 @@ componentgen(Node *nr, Node *nl)
 
 	nodl = *nl;
 	if(!cadable(nl)) {
-		if(nr == N || !cadable(nr))
+		if(nr != N && !cadable(nr))
 			goto no;
 		igen(nl, &nodl, N);
 		freel = 1;