minor perf optimization: remove this loop on macOS

src/feature_flags.zig

@@ -84,3 +84,5 @@ pub const disable_compression_in_http_client = false;
 //   Time (mean ± σ):     306.7 ms ±   6.1 ms    [User: 31.7 ms, System: 269.8 ms]
 //   Range (min … max):   299.5 ms … 318.8 ms    10 runs
 pub const use_libgit2 = true;
+
+pub const atomic_file_watcher = env.isLinux;

src/watcher.zig

@@ -532,10 +532,12 @@ pub fn NewWatcher(comptime ContextType: type) type {
             comptime copy_file_path: bool,
         ) !void {
             if (this.indexOf(hash)) |index| {
-                // On Linux, the file descriptor might be out of date.
-                if (fd > 0) {
-                    var fds = this.watchlist.items(.fd);
-                    fds[index] = fd;
+                if (comptime FeatureFlags.atomic_file_watcher) {
+                    // On Linux, the file descriptor might be out of date.
+                    if (fd > 0) {
+                        var fds = this.watchlist.items(.fd);
+                        fds[index] = fd;
+                    }
                 }
                 return;
             }