common: add windows.h where required, make gdi_handlers static

This patch has not been verified with VS/brew. It should be safe
hopefully. Compilation is fine with mingw32/spice-gtk.

canvas_base.h

@@ -27,6 +27,9 @@
 #include "lz.h"
 #include "region.h"
 #include "draw.h"
+#ifdef WIN32
+#include <windows.h>
+#endif
 
 #ifdef __cplusplus
 extern "C" {

canvas_utils.c

@@ -30,7 +30,7 @@
 #include "mem.h"
 
 #ifdef WIN32
-extern int gdi_handlers;
+static int gdi_handlers = 0;
 #endif
 
 #ifndef CANVAS_ERROR

canvas_utils.h

@@ -19,6 +19,10 @@
 #ifndef _H_CANVAS_UTILS
 #define _H_CANVAS_UTILS
 
+#ifdef WIN32
+#include <windows.h>
+#endif
+
 #include <spice/types.h>
 
 #include "pixman_utils.h"