[opus] [PATCH] opusfile configury fixes.

[Timothy B. Terriberry]

Ozkan Sezer wrote:
> In short, the existing version is fine with new autotools+libtool, yes,
> but the patch I suggested makes it to work on older setups too and w/o
> any added bugs. So I'd suggest that you consider it.

I'm not really competent enough to review autotools stuff, but I've 
asked Diego (who wrote our original autotools support) to review these. 
Not sure when exactly he can get to it, but I'll make sure it doesn't 
get dropped.