make: libcriu -- Use `obj-ext-src-y' target for pie/util-fd.c recompilation

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

lib/Makefile

 lib-so			+= libcriu
 obj-y			+= criu.o
+obj-ext-src-y		+= pie/util-fd.o
 
-cflags-y		+= -fPIC -Wa,--noexecstack -fno-stack-protector
-cflags-so		+= -rdynamic
 includes		+= -iquote $(obj)/../arch/$(ARCH)/include -iquote $(obj)/../include -iquote $(obj)/..
+cflags-y		+= $(includes) -fPIC -Wa,--noexecstack -fno-stack-protector
+cflags-so		+= -rdynamic
 
 .SECONDARY:
 
-#
-# We need util-fd.c to be re-compiled with
-# own flags, but our build engine can't
-# do such tricks yet, so write a rule
-# manually for a while.
-$(obj)/util-fd.o: $(obj)/../pie/util-fd.c
-	$(E) "  CC      " $@
-	$(Q) $(CC) -c $(cflags-y) $(CFLAGS) $(includes) $< -o $@
-
 ifneq ($(MAKECMDGOALS),clean)
 incdeps := y
 endif