SDL_windowsevents.c: fix build against older SDKs.
diff --git a/src/video/windows/SDL_windowsevents.c b/src/video/windows/SDL_windowsevents.c
index 6f4b5af..5370631 100644
--- a/src/video/windows/SDL_windowsevents.c
+++ b/src/video/windows/SDL_windowsevents.c
@@ -81,6 +81,16 @@
#define WM_UNICHAR 0x0109
#endif
+#ifndef IS_HIGH_SURROGATE
+#define IS_HIGH_SURROGATE(x) (((x) >= 0xd800) && ((x) <= 0xdbff))
+#endif
+#ifndef IS_LOW_SURROGATE
+#define IS_LOW_SURROGATE(x) (((x) >= 0xdc00) && ((x) <= 0xdfff))
+#endif
+#ifndef IS_SURROGATE_PAIR
+#define IS_SURROGATE_PAIR(h,l) (IS_HIGH_SURROGATE(h) && IS_LOW_SURROGATE(l))
+#endif
+
static SDL_Scancode
VKeytoScancodeFallback(WPARAM vkey)
{