cmd/compile: Move divconst_test out of test/bench/go1

This is necessary to avoid disrupting the go1 suite and gives
us a place to put other tests of basic compiler function and
correctness.

Change-Id: I36933819ff2bfe6a2121fff2be9a98efd2123d9a
Reviewed-on: https://go-review.googlesource.com/22597
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/test/README

+This directory holds small tests and benchmarks of code
+generated by the compiler.  This code is not for importing,
+and the tests are intended to verify that specific optimzations
+are applied and correct.

test/bench/go1/divconst_test.go → src/cmd/compile/internal/test/divconst_test.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package go1
+package test
 
 import (
 	"testing"

src/cmd/compile/internal/test/test.go

+package test