[PATCH] Check for existence of asprintf and vasprintf

[Ulf Hermann]

> these portability replacements are starting to get out of hand
> -mike
To what extent should elfutils be portable to non-GNU systems? My goal here is to port it to windows while minimizing the amount of external dependencies I have to add. The functions I have replaced so far are so trivial that I didn't consider it worthwhile to import things from gnulib in order to provide them.

Ulf