[RFC, take 2] Optional expat

[Eli Zaretskii]

> Date: Tue, 8 Aug 2006 14:07:06 -0400
> From: Daniel Jacobowitz <drow@false.org>
> 
> +@node Requirements
> +@section Requirements for building @value{GDBN}

I think this section would benefit from at least one @cindex entry.

> +use the @samp{--with-libexpat-prefix} option to specify its location.

I think @option is better than @samp here.

> +@cindex configuring @value{GDBN}
> +@cindex configuring @value{GDBN}, and source tree subdirectories

Please remove the second @cindex entry.  (Yes, I know you just moved
it from the current place.)  It's a bad idea to have several index
entries that begin with the same (long) string and point to the same
page.

Other than that, the doco patch is okay with me.