Add basic atmega32u support (#3337)

machine/atmega32u: add support for arduino leonardo

targets/arduino-leonardo.json

@@ -0,0 +1,10 @@
+{
+	"inherits": ["atmega32u4"],
+	"build-tags": ["arduino_leonardo"],
+	"ldflags": [
+		"--defsym=_bootloader_size=512",
+		"--defsym=_stack_size=512"
+	],
+	"flash-command": "avrdude -c avr109 -p atmega32u4 -b 57600 -P {port} -U flash:w:{hex}:i",
+	"emulator": "simavr -m atmega32u4 -f 16000000 {}"
+}

targets/atmega32u4.json

@@ -0,0 +1,11 @@
+{
+	"inherits": ["avr"],
+	"cpu": "atmega32u4",
+	"build-tags": ["atmega32u4", "avr5"],
+	"serial": "none",
+	"linkerscript": "src/device/avr/atmega32u4.ld",
+	"extra-files": [
+		"targets/avr.S",
+		"src/device/avr/atmega32u4.s"
+	]
+}