RFC: gcj extension directory support

[Per Bothner]

Anthony Green wrote:
> This is a compiler patch for adding support for an "extensions"
> directory.  I think it is correct, however we need a doc patch and a
> corresponding libjava patch to install libgcj.jar as
> $(prefix)/share/java/libgcj-VERSION.jar.

I noticed two problems:

#include <dirent.h> may not be portable.  It is a Posix.1 header,
not in ANSI C or some old Unix variants.  It probably should be
autoconf'd.

jcf_path_extdir_arg only seems to handle a single directory,
but according to the javac doc it should take a path (list of 
directories).  This isn't critical, and it's easy enough to fix
by adding an extra loop.
-- 
	--Per Bothner
per@bothner.com   http://www.bothner.com/per/