Add NDEBUG to CPPFLAGS if --enable-debug is unset.

configure

@@ -200,6 +200,8 @@ if [ -n "$DEBUG" -a "$DEBUG" != no -a "$DEBUG" != false ]; then
 	echo "Building with debugging symbols."
 	echo "CPPFLAGS += -DDEBUG" >>$CONFIG_MK
 	echo "CFLAGS +=	-g" >>$CONFIG_MK
+else
+	echo "CPPFLAGS+= -DNDEBUG" >>$CONFIG_MK
 fi
 
 case "$OS" in

include/xbps_api_impl.h

@@ -27,10 +27,6 @@
 #ifndef _XBPS_API_IMPL_H_
 #define _XBPS_API_IMPL_H_
 
-#ifndef DEBUG
-#define NDEBUG
-#endif
-
 #include <assert.h>
 #include <confuse.h>
 #define LIBXBPS_PRIVATE