Allow specifying NUM_SERIAL_PORTS explicitly

For AVR-based unittests, this was autodetected based on the registers
defined in `avr/io.h`, just like on an actual build. For non-AVR
targets, `NUM_SERIAL_PORTS` would always be 0.

Now, any existing define on the compiler commandline (i.e. from
`.arduino-ci.yaml`) takes precedence over any autodetected value.

Author: matthijskooijman

cpp/arduino/Godmode.h

@@ -20,16 +20,18 @@ unsigned long micros();
 
 #define MOCK_PINS_COUNT 256
 
-#if defined(UBRR3H)
-  #define NUM_SERIAL_PORTS 4
-#elif defined(UBRR2H)
-  #define NUM_SERIAL_PORTS 3
-#elif defined(UBRR1H)
-  #define NUM_SERIAL_PORTS 2
-#elif defined(UBRRH) || defined(UBRR0H)
-  #define NUM_SERIAL_PORTS 1
-#else
-  #define NUM_SERIAL_PORTS 0
+#if (!defined NUM_SERIAL_PORTS)
+  #if defined(UBRR3H)
+    #define NUM_SERIAL_PORTS 4
+  #elif defined(UBRR2H)
+    #define NUM_SERIAL_PORTS 3
+  #elif defined(UBRR1H)
+    #define NUM_SERIAL_PORTS 2
+  #elif defined(UBRRH) || defined(UBRR0H)
+    #define NUM_SERIAL_PORTS 1
+  #else
+    #define NUM_SERIAL_PORTS 0
+  #endif
 #endif
 
 class GodmodeState {

cpp/arduino/HardwareSerial.h

@@ -44,19 +44,19 @@ class HardwareSerial : public StreamTape
     operator bool() { return true; }
 };
 
-#if defined(UBRRH) || defined(UBRR0H)
+#if NUM_SERIAL_PORTS >= 1
   extern HardwareSerial Serial;
   #define HAVE_HWSERIAL0
 #endif
-#if defined(UBRR1H)
+#if NUM_SERIAL_PORTS >= 2
   extern HardwareSerial Serial1;
   #define HAVE_HWSERIAL1
 #endif
-#if defined(UBRR2H)
+#if NUM_SERIAL_PORTS >= 3
   extern HardwareSerial Serial2;
   #define HAVE_HWSERIAL2
 #endif
-#if defined(UBRR3H)
+#if NUM_SERIAL_PORTS >= 4
   extern HardwareSerial Serial3;
   #define HAVE_HWSERIAL3
 #endif