misc/cgo/testso: enable test on windows

Depends on CL 8715043 and CL 8676050.
Fixes #5273.

R=alex.brainman, r
CC=gobot, golang-dev
https://golang.org/cl/8764043

misc/cgo/testso/cgoso.c

+// Copyright 2013 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.
+
+#include "_cgo_export.h"
+
+#ifdef WIN32
+extern void setCallback(void *);
+void init() {
+	setCallback(goCallback);
+}
+#else
+void init() {}
+#endif

misc/cgo/testso/cgoso.go

@@ -6,11 +6,13 @@ package cgosotest
 
 /*
 #cgo LDFLAGS: -L. -lcgosotest
+void init(void);
 void sofunc(void);
 */
 import "C"
 
 func Test() {
+	C.init()
 	C.sofunc()
 }
 

misc/cgo/testso/cgoso_c.c

@@ -4,8 +4,22 @@
 
 // +build ignore
 
+#ifdef WIN32
+// A Windows DLL is unable to call an arbitrary function in
+// the main executable. Work around that by making the main
+// executable pass the callback function pointer to us.
+void (*goCallback)(void);
+__declspec(dllexport) void setCallback(void *f)
+{
+	goCallback = (void (*)())f;
+}
+__declspec(dllexport) void sofunc(void);
+#else
+extern void goCallback(void);
+void setCallback(void *f) { (void)f; }
+#endif
+
 void sofunc(void)
 {
-	extern void goCallback(void);
 	goCallback();
 }

misc/cgo/testso/test.bat

+:: Copyright 2013 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.
+
+@echo off
+
+gcc -c cgoso_c.c
+gcc -shared -o libcgosotest.dll cgoso_c.o
+if not exist libcgosotest.dll goto fail
+go build main.go
+if not exist main.exe goto fail
+main.exe
+goto :end
+
+:fail
+set FAIL=1
+:end
+del /F cgoso_c.o libcgosotest.dll main.exe 2>NUL

src/run.bat

@@ -87,6 +87,14 @@ echo # ..\misc\cgo\test
 go test ..\misc\cgo\test
 if errorlevel 1 goto fail
 echo.
+
+echo # ..\misc\cgo\testso
+cd ..\misc\cgo\testso
+set FAIL=0
+call test.bat
+cd ..\..\..\src
+if %FAIL%==1 goto fail
+echo.
 :nocgo
 
 echo # ..\doc\progs