make mymemmem available for linking

Author: julek-wolfssl

wolfssl/wolfcrypt/wc_port.h

@@ -1214,7 +1214,7 @@ WOLFSSL_ABI WOLFSSL_API int wolfCrypt_Cleanup(void);
 #ifndef WOLFSSL_LEANPSK
     char* mystrnstr(const char* s1, const char* s2, unsigned int n);
 #endif
-    void *mymemmem(const void *haystack, size_t haystacklen,
+    WOLFSSL_API void *mymemmem(const void *haystack, size_t haystacklen,
                  const void *needle, size_t needlelen);
 
 #ifndef FILE_BUFFER_SIZE