Respect the 'AR' environment variable.
--- a/Makefile.in
+++ b/Makefile.in
@@ -103,7 +103,7 @@ $(LIBOBJS):
 	$(CC) $(CFLAGS) $(CPPFLAGS) $(INCS) -c $(srcdir)/missing/$*.c
 
 libmissing.a: $(LIBOBJS)
-	ar -cr $@ $(LIBOBJS)
+	$(AR) -cr $@ $(LIBOBJS)
 	$(RANLIB) $@
 
 dsniff: $(HDRS) $(SRCS) $(OBJS) libmissing.a
--- a/configure.in
+++ b/configure.in
@@ -17,6 +17,7 @@ dnl Checks for programs.
 AC_PROG_CC
 AC_PROG_INSTALL
 AC_PROG_RANLIB
+AC_CHECK_PROG(AR,ar,ar)
 
 dnl Checks for header files.
 AC_PATH_XTRA