machine/esp32c3: implement USB_SERIAL for USBCDC communication

Signed-off-by: deadprogram <ron@hybridgroup.com>

src/runtime/runtime_esp32xx.go

@@ -10,22 +10,6 @@ import (
 
 type timeUnit int64
 
-func putchar(c byte) {
-	machine.Serial.WriteByte(c)
-}
-
-func getchar() byte {
-	for machine.Serial.Buffered() == 0 {
-		Gosched()
-	}
-	v, _ := machine.Serial.ReadByte()
-	return v
-}
-
-func buffered() int {
-	return machine.Serial.Buffered()
-}
-
 // Initialize .bss: zero-initialized global variables.
 // The .data section has already been loaded by the ROM bootloader.
 func clearbss() {
@@ -84,3 +68,19 @@ func sleepTicks(d timeUnit) {
 func exit(code int) {
 	abort()
 }
+
+func putchar(c byte) {
+	machine.Serial.WriteByte(c)
+}
+
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+		Gosched()
+	}
+	v, _ := machine.Serial.ReadByte()
+	return v
+}
+
+func buffered() int {
+	return machine.Serial.Buffered()
+}