serial global instance fix (espressif#1243)

Author: KEDARUMA-FANTASTIC

cores/esp32/HardwareSerial.cpp

@@ -5,7 +5,9 @@
 
 #include "HardwareSerial.h"
 
+#if !defined(NO_GLOBAL_INSTANCES) && !defined(NO_GLOBAL_SERIAL)
 HardwareSerial Serial(0);
+#endif
 
 HardwareSerial::HardwareSerial(int uart_nr) : _uart_nr(uart_nr), _uart(NULL) {}
 

cores/esp32/HardwareSerial.h

@@ -76,6 +76,8 @@ class HardwareSerial: public Stream
     uart_t* _uart;
 };
 
+#if !defined(NO_GLOBAL_INSTANCES) && !defined(NO_GLOBAL_SERIAL)
 extern HardwareSerial Serial;
+#endif
 
 #endif