Treat cpp string as UTF8

Fix arduino/Arduino#5277

Signed-off-by: Cristian Maglie <[email protected]>

Author: cmaglie

src/arduino.cc/builder/utils/utils.go

@@ -38,6 +38,7 @@ import (
 	"path/filepath"
 	"runtime"
 	"strings"
+	"unicode/utf8"
 
 	"arduino.cc/builder/constants"
 	"arduino.cc/builder/gohasissues"
@@ -443,23 +444,25 @@ func ParseCppString(line string) (string, string, bool) {
 			return "", line, false
 		}
 
-		switch line[i] {
+		c, width := utf8.DecodeRuneInString(line[i:])
+
+		switch c {
 		// Backslash, next character is used unmodified
 		case '\\':
-			i++
+			i += width
 			if i >= len(line) {
 				return "", line, false
 			}
 			res += string(line[i])
 			break
 		// Quote, end of string
 		case '"':
-			return res, line[i+1:], true
+			return res, line[i+width:], true
 		default:
-			res += string(line[i])
+			res += string(c)
 			break
 		}
 
-		i++
+		i += width
 	}
 }