Fix building on linux

Author: Silviu Caragea

c_src/utf8_cleanup.h

@@ -2,6 +2,7 @@
 #define ERLXML_C_SRC_UTF8_CLEANUP_H_
 
 #include <stdlib.h>
+#include <stdint.h>
 
 size_t utf8_cleanup(char* buffer, size_t length);