avrdude: Fix string encoding handling on Windows

src/avrdude/windows/utf8.h

@@ -0,0 +1,10 @@
+#ifndef SLIC3R_AVRDUDE_UTF8_H
+#define SLIC3R_AVRDUDE_UTF8_H
+
+#include <windows.h>
+
+extern char* wstr_to_utf8(LPWSTR wstr, int len);
+extern LPWSTR utf8_to_wstr(const char *str, int len);
+
+
+#endif  // SLIC3R_AVRDUDE_UTF8_H