Define NDEBUG for assert() if --enable-debug is not specified.

configure

@@ -199,11 +199,10 @@ fi
 
 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
 fi
 
-echo "CPPFLAGS +=	-DDEBUG" >>$CONFIG_MK
-
 case "$OS" in
 linux)
 	echo "CPPFLAGS += 	-D_XOPEN_SOURCE=700" >>$CONFIG_MK

include/xbps_api_impl.h

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