win32, ...: avoid including windows.h

Include the most specific header documented by MSDN instead.

src/output/plugins/WinmmOutputPlugin.cxx

@@ -28,6 +28,10 @@
 #include <array>
 #include <iterator>
 
+#include <handleapi.h>
+#include <synchapi.h>
+#include <winbase.h> // for INFINITE
+
 #include <stdlib.h>
 #include <string.h>
 

src/output/plugins/WinmmOutputPlugin.hxx

@@ -26,7 +26,7 @@
 
 #include "util/Compiler.h"
 
-#include <windows.h>
+#include <windef.h>
 #include <mmsystem.h>
 
 struct WinmmOutput;