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/bexport.go b/src/cmd/compile/internal/gc/bexport.go
index 8968ce8..f88afd2 100644
--- a/src/cmd/compile/internal/gc/bexport.go
+++ b/src/cmd/compile/internal/gc/bexport.go
@@ -742,7 +742,7 @@
 }
 
 func (p *exporter) paramList(params *Type, numbered bool) {
-	if !params.IsStruct() || !params.Funarg {
+	if !params.IsFuncArgStruct() {
 		Fatalf("exporter: parameter list expected")
 	}