runtime: windows callback code to match new func value representation

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/7393048

src/pkg/runtime/callback_windows_386.c

@@ -80,7 +80,7 @@ runtime·compilecallback(Eface fn, bool cleanstack)
 
 	// MOVL fn, AX
 	*p++ = 0xb8;
-	*(uint32*)p = (uint32)fn.data;
+	*(uint32*)p = (uint32)(*(byte**)fn.data);
 	p += 4;
 
 	// MOVL argsize, DX

src/pkg/runtime/callback_windows_amd64.c

@@ -78,7 +78,7 @@ runtime·compilecallback(Eface fn, bool /*cleanstack*/)
 	// MOVQ fn, AX
 	*p++ = 0x48;
 	*p++ = 0xb8;
-	*(uint64*)p = (uint64)fn.data;
+	*(uint64*)p = (uint64)(*(byte**)fn.data);
 	p += 8;
 	// PUSH AX
 	*p++ = 0x50;