test,misc: fix builders that do not support plugin

CL 406358 added test that use -buildmode=plugin. But plugin mode only
supports on some os/arch pairs, so this CL moving the test to
misc/cgo/testplugin directory instead.

Updates #52937

Change-Id: Iad049443c1f6539f6af1988bebd4dff56c6e1bf9
Reviewed-on: https://go-review.googlesource.com/c/go/+/406774
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

misc/cgo/testplugin/plugin_test.go

@@ -296,6 +296,10 @@ func TestIssue44956(t *testing.T) {
 	run(t, "./issue44956.exe")
 }
 
+func TestIssue52937(t *testing.T) {
+	goCmd(t, "build", "-buildmode=plugin", "-o", "issue52937.so", "./issue52937/main.go")
+}
+
 func TestForkExec(t *testing.T) {
 	// Issue 38824: importing the plugin package causes it hang in forkExec on darwin.
 

misc/cgo/testplugin/testdata/issue52937/main.go

@@ -1,8 +1,3 @@
-// build -buildmode=plugin
-
-//go:build !js
-// +build !js
-
 // Copyright 2022 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.