Fix redbean zip central directory lookup

This regression snuck in at some point. It resulted in the program
sometimes failing to load when the zip content was changed.

build/definitions.mk

@@ -137,6 +137,7 @@ MATHEMATICAL =								\
 	-fwrapv
 
 DEFAULT_CPPFLAGS =							\
+	-DMODE='"$(MODE)"'						\
 	-DIMAGE_BASE_VIRTUAL=$(IMAGE_BASE_VIRTUAL)			\
 	-nostdinc							\
 	-iquote.

build/gdb

@@ -0,0 +1,5 @@
+#!/bin/sh
+exec gdb -q -nh -i=mi $1                   \
+     -ex "set confirm off"                 \
+     -ex "add-symbol-file $1.dbg 0x401000" \
+     -ex "run"