fix: re-enable dune on older macos sdk's

by disabling watch mode on such versions

Signed-off-by: Rudi Grinberg <me@rgrinberg.com>

ps-id: dc8e96cc-61a9-4497-baac-0934b82efe6f

src/fsevents/fsevents_stubs.c

@@ -6,7 +6,7 @@
 #include <caml/mlvalues.h>
 #include <caml/threads.h>
 
-#if defined(__APPLE__)
+#if defined(__APPLE__) && __MAC_OS_X_VERSION_MAX_ALLOWED >= 100700
 
 #include <Availability.h>
 #include <CoreFoundation/CoreFoundation.h>
@@ -90,9 +90,10 @@ static void dune_fsevents_callback(const FSEventStreamRef streamRef,
     CFStringRef cf_path;
 #if __MAC_OS_X_VERSION_MAX_ALLOWED >= 101300
     CFDictionaryRef details = CFArrayGetValueAtIndex(eventPaths, i);
-    cf_path = CFDictionaryGetValue(details, kFSEventStreamEventExtendedDataPathKey);
+    cf_path =
+        CFDictionaryGetValue(details, kFSEventStreamEventExtendedDataPathKey);
 #else
-    cf_path = (CFStringRef) CFArrayGetValueAtIndex(eventPaths, i);
+    cf_path = (CFStringRef)CFArrayGetValueAtIndex(eventPaths, i);
 #endif
     CFIndex len = CFStringGetLength(cf_path);
     CFIndex byte_len;
@@ -331,7 +332,12 @@ CAMLprim value dune_fsevents_available(value unit) {
 
 #else
 
-static char *unavailable_message = "fsevents is only available on macos";
+static char *unavailable_message =
+#if defined(__APPLE__)
+    "upgrade your macos sdk to enable watch mode";
+#else
+    "fsevents is only available on macos";
+#endif
 
 CAMLprim value dune_fsevents_stop(value v_t) {
   caml_failwith(unavailable_message);