Add Makefile rule to generate .dir-locals.el file

It is good for company-mode, so it won’t die due to unknown include
directories.

.gitignore

@@ -100,3 +100,4 @@ Makefile.in
 /docs/reference/*/xml/
 /docs/reference/*/html/
 /gtk-doc.make
+.dir-locals.el

src/Makefile.am

@@ -36,3 +36,9 @@ astrognome_LDADD = $(SWE_GLIB_LIBS) $(GTK_LIBS) $(LIBXML_LIBS) $(LIBXSLT_LIBS) $
 astrognome_LDFLAGS = -rdynamic
 astrognome_CFLAGS = $(SWE_GLIB_CFLAGS) $(CFLAGS) $(GTK_CFLAGS) $(LIBXML_CFLAGS) $(LIBXSLT_CFLAGS) $(WEBKIT_CFLAGS) $(GDA_CFLAGS) $(PIXBUF_CFLAGS) $(RSVG_CFLAGS) -Wall
 
+# The following two lines generate a .dir-locals.el file, so
+# company-mode won’t die due to unknown includes
+.dir-locals.el:
+	@echo $(astrognome_CFLAGS) | ./gen-dir-locals-el.sh
+
+.PHONY: .dir-locals.el

src/gen-dir-locals-el.sh

@@ -0,0 +1,8 @@
+#! /bin/sh
+
+(echo -n "((nil . ((company-clang-arguments . ("
+for line in `cat - | sed -e 's/\s\+/\n/g' | grep '^-I' | sort | uniq`
+do
+    echo '"'$line'"'
+done
+echo ")))))") > .dir-locals.el