Use memcmp() instead of CRYPTO_memcmp() when fuzzing

Reviewed-by: Andy Polyakov <appro@openssl.org>
GH: #2633

crypto/cryptlib.c

@@ -321,6 +321,7 @@ void OPENSSL_die(const char *message, const char *file, int line)
  *
  * There are also assembler versions of this function.
  */
+# undef CRYPTO_memcmp
 int CRYPTO_memcmp(const void * in_a, const void * in_b, size_t len)
 {
     size_t i;

e_os.h

@@ -513,6 +513,10 @@ struct servent *getservbyname(const char *name, const char *proto);
 
 #define OSSL_NELEM(x)    (sizeof(x)/sizeof(x[0]))
 
+#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
+# define CRYPTO_memcmp memcmp
+#endif
+
 #ifdef  __cplusplus
 }
 #endif