add rule to create proxy

- otherwise some make commands aren't able to build the proxy because
  they ignore the LDFLAGS

hermit/tools/Makefile

@@ -4,7 +4,6 @@ NASMFLAGS = -fbin
 CC = gcc
 CFLAGS = -O2 -Wall
 HEXDUMP = hexdump
-LDFLAGS = -lelf
 PROXYFILES = proxy init.sh $(shell find ../usr/tests ../usr/benchmarks ../usr/openmpbench -type f -executable)
 
 # Prettify output
@@ -21,6 +20,10 @@ endif
 
 all: init.h proxy
 
+proxy: proxy.o
+	@echo [LD] $@
+	$Q$(CC) $(CFLAGS) -o $@ $< -lelf
+
 init.bin: init.asm
 	@echo [NASM] $@
 	$Q$(NASM) $(NASMFLAGS) -o $@ $<