make mingw happy (#182)

Storage class specifiers are not allowed in friend declarations. Maybe it's a MSVC dialect.

Author: zhuzeitou

highgui/src/display_win32.cpp

@@ -43,7 +43,7 @@ static inline void safeReleaseArray(T* &array) {
 	array = nullptr;
 }
 
-static LRESULT CALLBACK __globalWndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
+LRESULT CALLBACK __globalWndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
 {
 	if (g_wndBeingCreated) {
 		g_wndBeingCreated->m_hWnd = hWnd;

highgui/src/display_win32.h

@@ -16,7 +16,7 @@
 
 #pragma once
 
-#include <Windows.h>
+#include <windows.h>
 
 class SimpleWindow
 {
@@ -25,7 +25,7 @@ class SimpleWindow
 	virtual LRESULT windowProc(UINT msg, WPARAM wParam, LPARAM lParam);
 
 public:
-	friend static LRESULT CALLBACK __globalWndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);
+	friend LRESULT CALLBACK __globalWndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);
 
 	static double getDesktopDpiFactor();