doc: refactor common asciidoc dependencies

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/Makefile

@@ -139,6 +139,7 @@ ASCIIDOC_CONF = -f asciidoc.conf
 ASCIIDOC_COMMON = $(ASCIIDOC) $(ASCIIDOC_EXTRA) $(ASCIIDOC_CONF) \
 		-amanversion=$(GIT_VERSION) \
 		-amanmanual='Git Manual' -amansource='Git'
+ASCIIDOC_DEPS = asciidoc.conf asciidoctor-extensions.rb GIT-ASCIIDOCFLAGS
 TXT_TO_HTML = $(ASCIIDOC_COMMON) -b $(ASCIIDOC_HTML)
 TXT_TO_XML = $(ASCIIDOC_COMMON) -b $(ASCIIDOC_DOCBOOK)
 MANPAGE_XSL = manpage-normal.xsl
@@ -354,12 +355,12 @@ clean:
 	$(RM) manpage-base-url.xsl
 	$(RM) GIT-ASCIIDOCFLAGS
 
-$(MAN_HTML): %.html : %.txt asciidoc.conf asciidoctor-extensions.rb GIT-ASCIIDOCFLAGS
+$(MAN_HTML): %.html : %.txt $(ASCIIDOC_DEPS)
 	$(QUIET_ASCIIDOC)$(RM) $@+ $@ && \
 	$(TXT_TO_HTML) -d manpage -o $@+ $< && \
 	mv $@+ $@
 
-$(OBSOLETE_HTML): %.html : %.txto asciidoc.conf asciidoctor-extensions.rb GIT-ASCIIDOCFLAGS
+$(OBSOLETE_HTML): %.html : %.txto $(ASCIIDOC_DEPS)
 	$(QUIET_ASCIIDOC)$(RM) $@+ $@ && \
 	$(TXT_TO_HTML) -o $@+ $< && \
 	mv $@+ $@
@@ -371,7 +372,7 @@ manpage-base-url.xsl: manpage-base-url.xsl.in
 	$(QUIET_XMLTO)$(RM) $@ && \
 	$(XMLTO) -m $(MANPAGE_XSL) $(XMLTO_EXTRA) man $<
 
-%.xml : %.txt asciidoc.conf asciidoctor-extensions.rb GIT-ASCIIDOCFLAGS
+%.xml : %.txt $(ASCIIDOC_DEPS)
 	$(QUIET_ASCIIDOC)$(RM) $@+ $@ && \
 	$(TXT_TO_XML) -d manpage -o $@+ $< && \
 	mv $@+ $@