Makefile: Add LDFLAGS directive

This patch adds LDFLAGS directive to build with -static.
You can build in static mode like below:
$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi LDFLAGS=-static
Signed-off-by: Chanho Park <chanho61.park@samsung.com>
Signed-off-by: Myungjoo Ham <myungjoo.ham@samsung.com>
Acked-by: Alexander Kartashov <alekskartashov@parallels.com>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

Makefile

@@ -152,7 +152,7 @@ PROGRAM-BUILTINS	+= $(ARCH_DIR)/vdso-pie.o
 
 $(PROGRAM): $(SYSCALL-LIB) $(ARCH-LIB) $(PROGRAM-BUILTINS)
 	$(E) "  LINK    " $@
-	$(Q) $(CC) $(CFLAGS) $^ $(LIBS) -o $@
+	$(Q) $(CC) $(CFLAGS) $^ $(LIBS) $(LDFLAGS) -o $@
 
 zdtm: all
 	$(Q) $(MAKE) -C test/zdtm all