md5: use axTLS's own MD5 functions when available

lib/md5.c

@@ -157,6 +157,9 @@ static void MD5_Final(unsigned char digest[16], MD5_CTX *ctx)
     CryptReleaseContext(ctx->hCryptProv, 0);
 }
 
+#elif defined(USE_AXTLS)
+#include <axTLS/os_int.h>
+#include <axTLS/crypto.h>
 #else
 /* When no other crypto library is available we use this code segment */
 /*