cmd/compile: rewrite %1v and %2v formats to %S and %L (short and long)

- also consistently use %v instead of %s when we have a (gc) Formatter
- rewrite done automatically using Formats test in -u (update) mode
- manual update of format strings that were not single string constants
- updated fmt.go, fmt_test.go accordingly
- fmt_test: permit "%T" always

Change-Id: I8f0704286aba5704600ad0c4a4484005b79b905d
Reviewed-on: https://go-review.googlesource.com/28954
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -556,7 +556,7 @@ func overflow(v Val, t *Type) {
 	}
 
 	if doesoverflow(v, t) {
-		Yyerror("constant %s overflows %v", v, t)
+		Yyerror("constant %v overflows %v", v, t)
 	}
 }
 
@@ -1595,7 +1595,7 @@ func (n *Node) Convconst(con *Node, t *Type) {
 		var i int64
 		switch n.Val().Ctype() {
 		default:
-			Fatalf("convconst ctype=%d %2v", n.Val().Ctype(), t)
+			Fatalf("convconst ctype=%d %L", n.Val().Ctype(), t)
 
 		case CTINT, CTRUNE:
 			i = n.Int64()
@@ -1632,7 +1632,7 @@ func (n *Node) Convconst(con *Node, t *Type) {
 		return
 	}
 
-	Fatalf("convconst %2v constant", t)
+	Fatalf("convconst %L constant", t)
 }
 
 // complex multiply v *= rv