Fix up debian build

debian/changelog

 dropbear (2013.59-0.1) unstable; urgency=low
   * New upstream release.
+  * Build with DEB_BUILD_MAINT_OPTIONS = hardening=+all
  -- Matt Johnston <matt@ucc.asn.au>  Fri, 4 Oct 2013 22:54:00 +0800

debian/rules

 #!/usr/bin/make -f
+export DEB_BUILD_MAINT_OPTIONS = hardening=+all
+DPKG_EXPORT_BUILDFLAGS = 1
+include /usr/share/dpkg/buildflags.mk
+
 #export DH_OPTIONS
 DEB_HOST_GNU_TYPE ?=$(shell dpkg-architecture -qDEB_HOST_GNU_TYPE)
 DEB_BUILD_GNU_TYPE ?=$(shell dpkg-architecture -qDEB_BUILD_GNU_TYPE)
@@ -9,13 +13,6 @@ ifneq (,$(findstring nostrip,$(DEB_BUILD_OPTIONS)))
   STRIP =: nostrip
 endif
-CFLAGS =-Wall -g
-ifneq (,$(findstring noopt,$(DEB_BUILD_OPTIONS)))
-  CFLAGS +=-O0
-else
-  CFLAGS +=-O2
-endif
-
 CONFFLAGS =
 CC =gcc
 ifneq (,$(findstring diet,$(DEB_BUILD_OPTIONS)))