Fix Makefile for rst files

doc/Makefile

@@ -8,13 +8,23 @@ SPHINXPROJ    = flint
 SOURCEDIR     = source
 BUILDDIR      = build
 
+M4 := m4
+
+SRCS := $(wildcard $(SOURCEDIR)/*.rst.pp)
+OBJS := $(patsubst %.pp,%,$(SRCS))
+
 # Put it first so that "make" without argument is like "make help".
 help:
 	@$(SPHINXBUILD) -M help "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
 
-.PHONY: help Makefile
+preprocess: $(OBJS)
+
+%.rst: %.rst.pp
+	@$(M4) -I $(SOURCEDIR) $< > $@
+
+.PHONY: help Makefile preprocess
 
-# Catch-all target: route all unknown targets to Sphinx using the new
-# "make mode" option.  $(O) is meant as a shortcut for $(SPHINXOPTS).
-%: Makefile
-	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
+# # Catch-all target: route all unknown targets to Sphinx using the new
+# # "make mode" option.  $(O) is meant as a shortcut for $(SPHINXOPTS).
+# %: Makefile preprocess
+# 	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)