Cocoa: Fix compilation error on OS X 10.8

The occlusion state parts of NSWindow are OS X 10.9+ only but we still
(technically) support building for only 10.8.

Fixes #2161

(cherry picked from commit 5e4496cb42)

README.md

@@ -128,6 +128,8 @@ information on what to include when reporting a bug.
  - [Win32] Fix pkg-config for dynamic library on Windows (#2386, #2420)
  - [Win32] Bugfix: `glfwWaitEventsTimeout` did not return for some sent messages (#2408)
  - [Win32] Bugfix: XInput could reportedly provide invalid DPad bit masks (#2291)
+ - [Cocoa] Bugfix: Compilation failed on OS X 10.8 due to unconditional use of 10.9+
+   symbols (#2161)
  - [Wayland] Added improved fallback window decorations via libdecor (#1639,#1693)
  - [Wayland] Bugfix: Connecting a mouse after `glfwInit` would segfault (#1450)
  - [Wayland] Disabled alpha channel for opaque windows on systems lacking

src/cocoa_window.m

@@ -309,10 +309,15 @@ static const NSRange kEmptyRange = { NSNotFound, 0 };
 
 - (void)windowDidChangeOcclusionState:(NSNotification* )notification
 {
-    if ([window->ns.object occlusionState] & NSWindowOcclusionStateVisible)
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= 1090
-        window->ns.occluded = GLFW_FALSE;
+    if ([window->ns.object respondsToSelector:@selector(occlusionState)])
-    else
+    {
-        window->ns.occluded = GLFW_TRUE;
+        if ([window->ns.object occlusionState] & NSWindowOcclusionStateVisible)
+            window->ns.occluded = GLFW_FALSE;
+        else
+            window->ns.occluded = GLFW_TRUE;
+    }
+#endif
 }
 
 @end