Stop past timestamps from setting our system time RTC (#4704)

* Ignore attempts to set times in the past (before our build epoch)

* TRONK

platformio.ini

@@ -81,6 +81,7 @@ build_flags = -Wno-missing-field-initializers
   -DRADIOLIB_EXCLUDE_APRS
   -DRADIOLIB_EXCLUDE_LORAWAN
   -DMESHTASTIC_EXCLUDE_DROPZONE=1
+  -DBUILD_EPOCH=$UNIX_TIME
   ;-D OLED_PL
 
 monitor_speed = 115200

src/gps/RTC.cpp

@@ -109,6 +109,12 @@ bool perhapsSetRTC(RTCQuality q, const struct timeval *tv, bool forceUpdate)
     static uint32_t lastSetMsec = 0;
     uint32_t now = millis();
     uint32_t printableEpoch = tv->tv_sec; // Print lib only supports 32 bit but time_t can be 64 bit on some platforms
+#ifdef BUILD_EPOCH
+    if (tv->tv_sec < BUILD_EPOCH) {
+        LOG_WARN("Ignoring time (%ld) before build epoch (%ld)!\n", printableEpoch, BUILD_EPOCH);
+        return false;
+    }
+#endif
 
     bool shouldSet;
     if (forceUpdate) {