made openssl support optional (in configuration)

configure.seed

@@ -16,36 +16,37 @@ fi
 N2N_LIBS=
 
 AC_PROG_CC
-AC_CHECK_LIB([zstd], [ZSTD_compress])
 
-if test "x$ac_cv_lib_zstd_ZSTD_compress" != xyes; then
+AC_ARG_WITH([zstd],
+ [AS_HELP_STRING([--with-zstd],
+ [enable support for zstd])],
+ [],
+ [with_zstd=no])
+if test "x$with_zstd" != xno; then
+  AC_CHECK_LIB([zstd], [ZSTD_compress])
+  if test "x$ac_cv_lib_zstd_ZSTD_compress" != xyes; then
     AC_MSG_RESULT(Building n2n without ZSTD support)
-else
+  else
     AC_DEFINE([N2N_HAVE_ZSTD], [], [Have ZSTD support])
     N2N_LIBS="-lzstd ${N2N_LIBS}"
+  fi
 fi
 
-
 AC_ARG_WITH([openssl],
  [AS_HELP_STRING([--with-openssl],
  [enable support for OpenSSL])],
  [],
  [with_openssl=no])
-
 if test "x$with_openssl" != xno; then
-
   AC_CHECK_LIB([crypto], [AES_cbc_encrypt])
-
   if test "x$ac_cv_lib_crypto_AES_cbc_encrypt" != xyes; then
     AC_MSG_RESULT(OpenSSL not present)
   else
     AC_DEFINE([HAVE_OPENSSL_1_0], [], [OpenSSL 1.0 is present])
     N2N_LIBS="-lcrypto ${N2N_LIBS}"
   fi
-
   OLD_CFLAGS="${CFLAGS}"
   OLD_LDFLAGS="${LDFLAGS}"
-
   CFLAGS="${CFLAGS} -I/usr/local/opt/openssl@1.1/include"
   LDFLAGS="${LDFLAGS} -L/usr/local/opt/openssl@1.1/lib/"
   AC_CHECK_LIB([crypto], [EVP_CIPHER_CTX_reset])
@@ -55,7 +56,6 @@ if test "x$with_openssl" != xno; then
   else
     AC_DEFINE([HAVE_OPENSSL_1_1], [], [OpenSSL 1.1 is present])
   fi
-
 fi
 
 AC_CHECK_LIB([pcap], [pcap_open_live], pcap=true)