always print debug output to both serial and segger debug port

cc @mc-hamster, this  makes USE_SEGGER optional on nrf52 targets

src/RedirectablePrint.cpp

@@ -1,4 +1,5 @@
 #include "RedirectablePrint.h"
+#include "configuration.h"
 #include <assert.h>
 
 /**
@@ -10,4 +11,14 @@ void RedirectablePrint::setDestination(Print *_dest)
 {
     assert(_dest);
     dest = _dest;
+}
+
+size_t RedirectablePrint::write(uint8_t c)
+{
+#ifdef SEGGER_STDOUT_CH
+    SEGGER_RTT_PutCharSkip(SEGGER_STDOUT_CH, c);
+#endif
+
+    dest->write(c);
+    return 1; // We always claim one was written, rather than trusting what the serial port said (which could be zero)
 }