cmd/internal/gc: make class uint8 throughout

This prevents conversion noise.

No functional changes. Passes toolstash -cmp.

Change-Id: I238adf28680f875217827931a689ce7f19a9b371
Reviewed-on: https://go-review.googlesource.com/8164
Reviewed-by: David Chase <drchase@google.com>
diff --git a/src/cmd/internal/gc/dcl.go b/src/cmd/internal/gc/dcl.go
index 846ec7d..c8375dd 100644
--- a/src/cmd/internal/gc/dcl.go
+++ b/src/cmd/internal/gc/dcl.go
@@ -165,7 +165,7 @@
 
 var declare_typegen int
 
-func declare(n *Node, ctxt int) {
+func declare(n *Node, ctxt uint8) {
 	if ctxt == PDISCARD {
 		return
 	}
@@ -232,7 +232,7 @@
 	autoexport(n, ctxt)
 }
 
-func addvar(n *Node, t *Type, ctxt int) {
+func addvar(n *Node, t *Type, ctxt uint8) {
 	if n == nil || n.Sym == nil || (n.Op != ONAME && n.Op != ONONAME) || t == nil {
 		Fatal("addvar: n=%v t=%v nil", Nconv(n, 0), Tconv(t, 0))
 	}