Add _GNU_SOURCE to compile options for Linux

Makefile.Linux

@@ -10,7 +10,7 @@
 BUILDDIR = ../bin/
 CC = gcc
 
-CFLAGS = -g -O2 -fno-strict-aliasing -c -pthread -DWITHSPLICE -DGETHOSTBYNAME_R -D_THREAD_SAFE -D_REENTRANT -DNOODBC -DWITH_STD_MALLOC -DFD_SETSIZE=4096 -DWITH_POLL -DWITH_NETFILTER
+CFLAGS = -g -O2 -fno-strict-aliasing -c -pthread -DWITHSPLICE -D_GNU_SOURCE -DGETHOSTBYNAME_R -D_THREAD_SAFE -D_REENTRANT -DNOODBC -DWITH_STD_MALLOC -DFD_SETSIZE=4096 -DWITH_POLL -DWITH_NETFILTER
 COUT = -o 
 LN = gcc
 DCFLAGS = -fpic