Care that CFLAGS set in debian/rules are honoured.

Index: xymon/build/Makefile.Linux
===================================================================
--- xymon.orig/build/Makefile.Linux	2012-06-12 17:12:05.000000000 +0200
+++ xymon/build/Makefile.Linux	2012-06-12 18:29:17.000000000 +0200
@@ -7,12 +7,7 @@
 
 # Compile flags for normal build
 CC = gcc
-GCCVER := $(shell gcc -dumpversion|cut -d. -f1)
-ifeq ($(GCCVER),4)
-   CFLAGS = -g -O2 -Wall -Wno-unused -Wno-pointer-sign -D_REENTRANT $(LFSDEF) $(OSDEF)
-else
-   CFLAGS = -g -O2 -Wall -Wno-unused -D_REENTRANT $(LFSDEF) $(OSDEF)
-endif
+CFLAGS += -Wall -Wno-unused -Wno-pointer-sign -D_REENTRANT $(LFSDEF) $(OSDEF)
 
 ifndef PKGBUILD
 RPATH = -Wl,--rpath,
