cmd/compile: encapsulate reads of gc.Type.Funarg

Changes generated with eg and then manually
checked and in some cases simplified.

Passes toolstash -cmp.

Change-Id: I2119f37f003368ce1884d2863b406d6ffbfe38c7
Reviewed-on: https://go-review.googlesource.com/21563
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
diff --git a/src/cmd/compile/internal/gc/walk.go b/src/cmd/compile/internal/gc/walk.go
index b7edae5..392dae0 100644
--- a/src/cmd/compile/internal/gc/walk.go
+++ b/src/cmd/compile/internal/gc/walk.go
@@ -1783,7 +1783,7 @@
 	var nn []*Node
 
 	// f(g()) where g has multiple return values
-	if r != nil && len(lr) <= 1 && r.Type.IsStruct() && r.Type.Funarg {
+	if r != nil && len(lr) <= 1 && r.Type.IsFuncArgStruct() {
 		// optimization - can do block copy
 		if eqtypenoname(r.Type, nl) {
 			arg := nodarg(nl, fp)