Added test case for Windows cpp building.

test cases/windows/3 cpp/meson.build

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

test cases/windows/3 cpp/prog.cpp

@@ -0,0 +1,7 @@
+#include<windows.h>
+
+class Foo;
+
+int main(int argc, char **argv) {
+    return 0;
+}