cmd/compile: split dumptypestructs further

This is preparatory cleanup to make future changes clearer.

Change-Id: I20fb9c78257de61b8bd096fce6b1e751995c01f2
Reviewed-on: https://go-review.googlesource.com/41818
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/compile/internal/gc/obj.go

@@ -137,7 +137,8 @@ func dumpobj1(outfile string, mode int) {
 
 	dumpglobls()
 	addptabs()
-	dumptypestructs(externdcl)
+	addsignats(externdcl)
+	dumpsignats()
 	dumptabs()
 	dumpimportstrings()
 	dumpbasictypes()

src/cmd/compile/internal/gc/reflect.go

@@ -1404,14 +1404,16 @@ func addsignat(t *types.Type) {
 	signatlist[formalType(t)] = true
 }
 
-func dumptypestructs(dcls []*Node) {
+func addsignats(dcls []*Node) {
 	// copy types from dcl list to signatlist
 	for _, n := range dcls {
 		if n.Op == OTYPE {
 			addsignat(n.Type)
 		}
 	}
+}
 
+func dumpsignats() {
 	// Process signatlist. Use a loop, as dtypesym adds
 	// entries to signatlist while it is being processed.
 	signats := make([]typeAndStr, len(signatlist))