fix(utils): Add header guard

Author: howjmay

accelerator/apis.c

@@ -96,7 +96,7 @@ status_t api_find_transactions_by_tag(
     goto done;
   }
 
-  char *req_tag = (char*)malloc((NUM_TRYTES_TAG + 1) * sizeof(char));
+  char* req_tag = (char*)malloc((NUM_TRYTES_TAG + 1) * sizeof(char));
   int obj_len = strlen(obj);
 
   if (obj_len == NUM_TRYTES_TAG) {

utils/fill_nines.h

@@ -1,6 +1,13 @@
+#ifndef UTILS_FILL_NINES_H_
+#define UTILS_FILL_NINES_H_
+
 #include "accelerator/errors.h"
 #include "cclient/types/types.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /**
  * @brief Patch input string with nines into assigned length.
  *
@@ -14,3 +21,8 @@
  */
 status_t fill_nines(char* new_str, const char* const old_str,
                     size_t new_str_len);
+#ifdef __cplusplus
+}
+#endif
+
+#endif  // UTILS_FILL_NINES_H_