Add a .dir-locals.el file.

* .dir-locals.el: New file.
* Makefile.am (EXTRA_DIST): Distribute it.

.dir-locals.el

+((nil . ((whitespace-action . '(auto-cleanup))
+	 (whitespace-style . '(trailing lines-tail))
+	 (require-final-newline . t)))
+ (c++-mode . ((c-default-style . "gnu")
+	      (indent-tab-mode . t)
+	      (tab-width . 8)
+	      (fill-column . 70))))

Makefile.am

@@ -42,7 +42,7 @@ UTF8 = utf8/doc/ReleaseNotes utf8/doc/utf8cpp.html utf8/utf8.h	\
 
 ACLOCAL_AMFLAGS = -I m4
 EXTRA_DIST = HACKING ChangeLog.1 tools/gitlog-to-changelog tools/help2man \
-	     $(UTF8) m4/gnulib-cache.m4
+	     $(UTF8) m4/gnulib-cache.m4 .dir-locals.el
 
 dist-hook: gen-ChangeLog