build: disable assertions in release builds

refs #2139

Change-Id: Id4cc0b360848d06a0d1e5759cf2017cd1b4227ec
diff --git a/wscript b/wscript
index 8baa805..d2aff10 100644
--- a/wscript
+++ b/wscript
@@ -105,6 +105,10 @@
 
     conf.define('DEFAULT_CONFIG_FILE', '%s/ndn/nfd.conf' % conf.env['SYSCONFDIR'])
 
+    # disable assertions in release builds
+    if not conf.options.debug:
+        conf.define('NDEBUG', 1)
+
     conf.write_config_header('config.hpp')
 
 def build(bld):