Define AR to help with lua cross-compilation

Closes #997

deps/Makefile

@@ -60,10 +60,15 @@ endif
 
 LUA_CFLAGS+= -O2 -Wall -DLUA_ANSI $(CFLAGS)
 LUA_LDFLAGS+= $(LDFLAGS)
+# lua's Makefile defines AR="ar rcu", which is unusual, and makes it more
+# challenging to cross-compile lua (and redis).  These defines make it easier
+# to fit redis into cross-compilation environments, which typically set AR.
+AR=ar
+ARFLAGS=rcu
 
 lua: .make-prerequisites
 	@printf '%b %b\n' $(MAKECOLOR)MAKE$(ENDCOLOR) $(BINCOLOR)$@$(ENDCOLOR)
-	cd lua/src && $(MAKE) all CFLAGS="$(LUA_CFLAGS)" MYLDFLAGS="$(LUA_LDFLAGS)"
+	cd lua/src && $(MAKE) all CFLAGS="$(LUA_CFLAGS)" MYLDFLAGS="$(LUA_LDFLAGS)" AR="$(AR) $(ARFLAGS)"
 
 .PHONY: lua