Work around BGB going back in time

BGB has a rather minor bug regardling its linking capabilities causing
the connection to end prematurely.

source/main.c

@@ -392,6 +392,16 @@ void bgb_loop_timestamp(void *user, uint32_t t)
 {
     // Update the timestamp sent by the emulator
     struct mobile_user *mobile = (struct mobile_user *)user;
+
+    // Attempt to detect the clock going back in time
+    // This is probably a BGB bug, caused by enabling some options, such as
+    //   the "break on ld d,d" option.
+    if (((mobile->bgb_clock - t) & 0x7FFFFFFF) < 0x100) {
+        fprintf(stderr, "[BUG] Emulator went back in time? "
+                "old: 0x%08X; new: 0x%08X\n", mobile->bgb_clock, t);
+        return;
+    }
+
     mobile->bgb_clock = t;
     bgb_loop_action(mobile);
 }