[HardwareSerial] Fix ambiguous call of overloaded function

```
error: call of overloaded 'HardwareSerial(int, int)' is ambiguous`

    1 | HardwareSerial Serialx(0, 1);
      |                                  ^
In file included from cores/arduino/WSerial.h:5,
                 from cores/arduino/wiring.h:47,
                 from cores/arduino/Arduino.h:32,
                 from sketch_jan27b.ino.cpp:1:
cores/arduino/HardwareSerial.h:106:5: note: candidate: 'HardwareSerial::HardwareSerial(void*, bool)'
  106 |     HardwareSerial(void *peripheral, bool halfDuplex = false);
      |     ^~~~~~~~~~~~~~
cores/arduino/HardwareSerial.h:104:5: note: candidate: 'HardwareSerial::HardwareSerial(uint32_t, uint32_t)'
  104 |     HardwareSerial(uint32_t _rx, uint32_t _tx);
      |     ^~~~~~~~~~~~~~
```

When the Rx Pin is 0 then the compiler doesn't know which constructor
to use as 0 can be interpreted like NULL. So both of them are valid:
 HardwareSerial(uint32_t _rx, uint32_t _tx);
 HardwareSerial(void *peripheral, bool halfDuplex = false);

Defining an explicit type avoid this issue.

Signed-off-by: Frederic Pillon <frederic.pillon@st.com>

Author: fpistm

cores/arduino/HardwareSerial.cpp

@@ -116,7 +116,7 @@ HardwareSerial::HardwareSerial(PinName _rx, PinName _tx)
   init(_rx, _tx);
 }
 
-HardwareSerial::HardwareSerial(void *peripheral, bool halfDuplex)
+HardwareSerial::HardwareSerial(void *peripheral, HalfDuplexMode_t halfDuplex)
 {
   // If PIN_SERIALy_RX is not defined assume half-duplex
   _serial.pin_rx = NC;
@@ -247,7 +247,7 @@ HardwareSerial::HardwareSerial(void *peripheral, bool halfDuplex)
                           _serial.pin_rx = pinmap_pin(peripheral, PinMap_UART_RX);
                           _serial.pin_tx = pinmap_pin(peripheral, PinMap_UART_TX);
                         }
-  if (halfDuplex) {
+  if (halfDuplex == HALF_DUPLEX_ENABLED) {
     _serial.pin_rx = NC;
   }
   init(_serial.pin_rx, _serial.pin_tx);

cores/arduino/HardwareSerial.h

@@ -57,6 +57,15 @@ typedef uint16_t rx_buffer_index_t;
 typedef uint8_t rx_buffer_index_t;
 #endif
 
+// A bool should be enough for this
+// But it brings an build error due to ambiguous
+// call of overloaded HardwareSerial(int, int)
+// So defining a dedicated type
+typedef enum {
+  HALF_DUPLEX_DISABLED,
+  HALF_DUPLEX_ENABLED
+} HalfDuplexMode_t;
+
 // Define config for Serial.begin(baud, config);
 // below configs are not supported by STM32
 //#define SERIAL_5N1 0x00
@@ -103,7 +112,7 @@ class HardwareSerial : public Stream {
   public:
     HardwareSerial(uint32_t _rx, uint32_t _tx);
     HardwareSerial(PinName _rx, PinName _tx);
-    HardwareSerial(void *peripheral, bool halfDuplex = false);
+    HardwareSerial(void *peripheral, HalfDuplexMode_t halfDuplex = HALF_DUPLEX_DISABLED);
     HardwareSerial(uint32_t _rxtx);
     HardwareSerial(PinName _rxtx);
     void begin(unsigned long baud)

keywords.txt

@@ -270,6 +270,8 @@ PIN_WIRE_SCL	LITERAL1
 HardwareSerial	KEYWORD2
 setRx	KEYWORD2
 setTx	KEYWORD2
+HALF_DUPLEX_DISABLED	LITERAL1
+HALF_DUPLEX_ENABLED	LITERAL1
 setHalfDuplex	KEYWORD2
 isHalfDuplex	KEYWORD2
 enableHalfDuplexRx	KEYWORD2