cmd/compile: simplify less with non-negative number and constant 0 or 1

The most common cases:
len(s) > 0
len(s) < 1

and they can be simplified to:
len(s) != 0
len(s) == 0

Fixes #48054

Change-Id: I16e5b0cffcfab62a4acc2a09977a6cd3543dd000
Reviewed-on: https://go-review.googlesource.com/c/go/+/346050
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

test/codegen/issue48054.go

@@ -0,0 +1,31 @@
+// asmcheck
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+func a(n string) bool {
+	// arm64:"CBZ"
+	if len(n) > 0 {
+		return true
+	}
+	return false
+}
+
+func a2(n []int) bool {
+	// arm64:"CBZ"
+	if len(n) > 0 {
+		return true
+	}
+	return false
+}
+
+func a3(n []int) bool {
+	// amd64:"TESTQ"
+	if len(n) < 1 {
+		return true
+	}
+	return false
+}