access: file: properly report local files on Darwin

While Darwin implements fstatvfs, the statvfs structures f_flag
field is only defined to contain two flags, ST_RDONLY and ST_NOSUID.
So the check for MNT_LOCAL would always be false, reporting all files
as non-local.

To mitigate that, on Darwin we can just use fstatfs and check
statfs.f_flags for MNT_LOCAL.

modules/access/file.c

@@ -75,7 +75,19 @@ typedef struct
 #if !defined (_WIN32) && !defined (__OS2__)
 static bool IsRemote (int fd)
 {
-#if defined (HAVE_FSTATVFS) && defined (MNT_LOCAL)
+#if defined(__APPLE__)
+    /* This has to preceed the general fstatvfs implmentation below,
+     * as even though Darwin has fstatvfs, it does not expose the
+     * MNT_LOCAL in the statvfs.f_flag field.
+     */
+    struct statfs sfs;
+
+    if (fstatfs (fd, &sfs))
+        return false;
+
+    return !((sfs.f_flags & MNT_LOCAL) == MNT_LOCAL);
+
+#elif defined (HAVE_FSTATVFS) && defined (MNT_LOCAL)
     struct statvfs stf;
 
     if (fstatvfs (fd, &stf))