cmd/5g, cmd/8g: fix build

The test added in CL 63630043 fails on 5g and 8g because they
were not emitting the VARDEF instruction when clearing a fat
value by clearing the components. 6g had the call in the right place.

Hooray tests.

TBR=iant
CC=golang-codereviews
https://golang.org/cl/63660043

src/cmd/5g/ggen.c

@@ -766,14 +766,13 @@ clearfat(Node *nl)
 	if(debug['g'])
 		dump("\nclearfat", nl);
 
+	gvardef(nl);
 
 	w = nl->type->width;
 	// Avoid taking the address for simple enough types.
 	if(componentgen(N, nl))
 		return;
 
-	gvardef(nl);
-
 	c = w % 4;	// bytes
 	q = w / 4;	// quads
 

src/cmd/8g/ggen.c

@@ -73,13 +73,13 @@ clearfat(Node *nl)
 	if(debug['g'])
 		dump("\nclearfat", nl);
 
+	gvardef(nl);
+
 	w = nl->type->width;
 	// Avoid taking the address for simple enough types.
 	if(componentgen(N, nl))
 		return;
 
-	gvardef(nl);
-
 	c = w % 4;	// bytes
 	q = w / 4;	// quads