docs/Makefile: Introduce GENERATE_PANDOC_RULE_RAW

We are going to want to format SUPPORT.md which does not match the
filename patterns in docs/.  So provide a way to make an ad-hoc rule
using pandoc with the standard options.

No functional change in this patch.

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
Release-acked-by: Juergen Gross <jgross@suse.com>
Acked-by: Lars Kurth <lars.kurth@citrix.com>

docs/Makefile

@@ -237,17 +237,18 @@ txt/%.txt: %.markdown
 	$(INSTALL_DATA) $< $@
 
 # Metarule for generating pandoc rules.
-define GENERATE_PANDOC_RULE
-# $(1) is the target documentation format. $(2) is the source format.
-
-$(1)/%.$(1): %.$(2)
+define GENERATE_PANDOC_RULE_RAW
+$(1): $(2)
 ifneq ($(PANDOC),)
 	@$(INSTALL_DIR) $$(@D)
 	$(PANDOC) --number-sections --toc --standalone $$< --output $$@
 else
 	@echo "pandoc not installed; skipping $$@"
 endif
-
+endef
+define GENERATE_PANDOC_RULE
+# $(1) is the target documentation format. $(2) is the source format.
+$(call GENERATE_PANDOC_RULE_RAW,$(1)/%.$(1),%.$(2))
 endef
 $(eval $(call GENERATE_PANDOC_RULE,pdf,pandoc))   # pdf/%.pdf: %.pandoc
 $(eval $(call GENERATE_PANDOC_RULE,txt,pandoc))   # txt/%.txt: %.pandoc