at: fix configure cache issue with flex

Make sure flex is built before at if enabled, so it correctly detects
it and doesn't populate tgt-config.cache with invalid values.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

CHANGES

@@ -18,7 +18,7 @@
 	New packages: cgilua, copas, coxpcall, ffmpeg, libsvgtiny,
 	luafilesystem, luasocket, rings, wsapi, xavante, xterm
 
-	Updated/fixed packages: alsa-lib, alsamixergui, avahi,
+	Updated/fixed packages: alsa-lib, alsamixergui, at, avahi,
 	berkeleydb, bash, blackbox, busybox, bzip2, cdrkit, cmake,
 	dash, dhcp, dialog, diffutils, distcc, dmalloc, dnsmasq,
 	dropbear, e2fsprogs, fbv, file, flex, fontconfig, gawk, gmpc,

package/at/at.mk

@@ -12,6 +12,8 @@ AT_INSTALL_TARGET = YES
 # no install-strip / install-exec
 AT_INSTALL_TARGET_OPT = DESTDIR=$(TARGET_DIR) install
 
+AT_DEPENDENCIES = $(if $(BR2_PACKAGE_FLEX),flex)
+
 AT_CONF_OPT = \
         --with-jobdir=/var/spool/cron/atjobs \
         --with-atspool=/var/spool/cron/atspool \