Added test case for C++ app using winmain.

test cases/windows/4 winmaincpp/meson.build

@@ -0,0 +1,4 @@
+project('winmaincpp', 'cxx')
+
+exe = executable('prog', 'prog.cpp')
+add_test('winmaincpp', exe)

test cases/windows/4 winmaincpp/prog.cpp

@@ -0,0 +1,12 @@
+#include<windows.h>
+
+class Foo;
+
+int APIENTRY
+WinMain(
+    HINSTANCE hInstance,
+    HINSTANCE hPrevInstance,
+    LPSTR lpszCmdLine,
+    int nCmdShow) {
+    return 0;
+}