example: remove pkg-config in Makefile.

Because pkg-config(version before 0.28) reordered -Wl,--whole-archive -Wl,--no-whole-archive not to surround the dpdk libraries, so we remove pkg-config and do it ourselves.

example/Makefile

@@ -1,8 +1,14 @@
-LIBS = $(shell pkg-config --define-variable=TOPDIR=${CURDIR}/.. --libs f-stack.pc)
+LIBS+= -L${FF_PATH}/lib -L${FF_DPDK}/lib -Wl,--whole-archive,-lfstack,--no-whole-archive
+LIBS+= -g -Wl,--no-as-needed -fvisibility=default -pthread -lm -lrt
+LIBS+= -Wl,--whole-archive -lrte_pmd_vmxnet3_uio -lrte_pmd_i40e -lrte_pmd_ixgbe -lrte_pmd_e1000 -lrte_pmd_ring
+LIBS+= -Wl,--whole-archive -lrte_hash -lrte_kvargs -Wl,-lrte_mbuf -lethdev -lrte_eal -Wl,-lrte_mempool
+LIBS+= -lrte_ring -lrte_cmdline -lrte_cfgfile -lrte_kni -lrte_timer -Wl,-lrte_pmd_virtio
+LIBS+= -Wl,--no-whole-archive -lrt -lm -ldl -lm -lcrypto
+
 TARGET="helloworld"
 all:
 	cc -O -gdwarf-2  -I../lib -o ${TARGET} main.c ${LIBS}
 
 .PHONY: clean
 clean:
-	rm -f *.o ${TARGET}
+	rm -f *.o ${TARGET}