winhttp: Add stub for WinHttpCheckPlatform.

dlls/winhttp/main.c

@@ -82,3 +82,10 @@ HRESULT WINAPI DllUnregisterServer(void)
     FIXME("()\n");
     return S_OK;
 }
+
+BOOL WINAPI WinHttpCheckPlatform(void)
+{
+    FIXME("stub\n");
+    SetLastError(ERROR_NOT_SUPPORTED);
+    return FALSE;
+}

dlls/winhttp/winhttp.spec

@@ -3,7 +3,7 @@
 @ stdcall -private DllRegisterServer()
 @ stdcall -private DllUnregisterServer()
 @ stub WinHttpAddRequestHeaders
-@ stub WinHttpCheckPlatform
+@ stdcall WinHttpCheckPlatform()
 @ stub WinHttpCloseHandle
 @ stub WinHttpConnect
 @ stub WinHttpCrackUrl