Makefile: mark perllibdir as a .PHONY target

This target should be marked as .PHONY, just like other targets that
exist only for their side effects that do not create filesystem
entities with the same name.

Signed-off-by: Christian Hesse <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: eworm-de

Makefile

@@ -1973,6 +1973,7 @@ GIT-PERL-DEFINES: FORCE
 		echo "$$FLAGS" >$@; \
 	    fi
 
+.PHONY: perllibdir
 perllibdir:
 	@echo '$(perllibdir_SQ)'