Fix NO_GLOBAL_INSTANCES for Serial ports (#8184)

Author: paulocsanz

cores/esp8266/HardwareSerial.cpp

@@ -35,9 +35,6 @@
 
 // SerialEvent functions are weak, so when the user doesn't define them,
 // the linker just sets their address to 0 (which is checked below).
-// The Serialx_available is just a wrapper around Serialx.available(),
-// but we can refer to it weakly so we don't pull in the entire
-// HardwareSerial instance if the user doesn't also refer to it.
 void serialEvent() __attribute__((weak));
 
 HardwareSerial::HardwareSerial(int uart_nr)

cores/esp8266/HardwareSerial.h

@@ -233,8 +233,12 @@ class HardwareSerial: public Stream
     size_t _rx_size;
 };
 
+#if !defined(NO_GLOBAL_INSTANCES) && !defined(NO_GLOBAL_SERIAL)
 extern HardwareSerial Serial;
+#endif
+#if !defined(NO_GLOBAL_INSTANCES) && !defined(NO_GLOBAL_SERIAL1)
 extern HardwareSerial Serial1;
+#endif
 
 extern void serialEventRun(void) __attribute__((weak));
 

libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.cpp

@@ -849,6 +849,10 @@ bool HTTPClient::connect(void)
 {
     if(_reuse && _canReuse && connected()) {
         DEBUG_HTTPCLIENT("[HTTP-Client] connect: already connected, reusing connection\n");
+
+#if defined(NO_GLOBAL_INSTANCES) || defined(NO_GLOBAL_STREAMDEV)
+        StreamNull devnull;
+#endif
         _client->sendAvailable(devnull); // clear _client's output (all of it, no timeout)
         return true;
     }