Meaning of @:

[Ewan Delanoy]

     Below is the "bootstrap" rule in gcc5.2.0's Makefile. What I don't
   get is the meaning
   of the @: at the beginning of the seventh line. I couldn't find it in
   the manual.
   I only know that @ before a shell command makes that command executed
   but not displayed,
   but why add the : ?


   .PHONY: bootstrap bootstrap-lean
   bootstrap:
       echo stage3 > stage_final
       @r=`${PWD_COMMAND}`; export r; \
       s=`cd $(srcdir); ${PWD_COMMAND}`; export s; \
       $(MAKE) $(RECURSE_FLAGS_TO_PASS) stage3-bubble
       @: $(MAKE); $(unstage)
       @r=`${PWD_COMMAND}`; export r; \
       s=`cd $(srcdir); ${PWD_COMMAND}`; export s; \
       TFLAGS="$(STAGE3_TFLAGS)"; \
       $(MAKE) $(TARGET_FLAGS_TO_PASS) all-host all-target