Fix build on macOS High Sierra

Check for >= 10.14 using Availability.h to use the accessibilityRole
callback which does not seem to be available in 10.13.

Signed-off-by: Rafael Kitover <rkitover@gmail.com>

glfw/cocoa_window.m

@@ -29,6 +29,7 @@
 #include "internal.h"
 #include "../kitty/monotonic.h"
 
+#include <Availability.h>
 #include <float.h>
 #include <string.h>
 
@@ -1551,11 +1552,15 @@ - (BOOL)isAccessibilitySelectorAllowed:(SEL)selector
     return NO;
 }
 
+#if (TARGET_OS_OSX && __MAC_OS_X_VERSION_MIN_REQUIRED >= 101400)
+
 - (NSAccessibilityRole)accessibilityRole
 {
     return NSAccessibilityTextAreaRole;
 }
 
+#endif
+
 - (NSString *)accessibilitySelectedText
 {
     NSString *text = nil;