I’m posting this mostly as a note to myself.
When trying to build the pecl sphinx extension, ran into problems because I could not build libsphinxclient.
It looks like the bug causing that problem has been around for at least a year, but at least the fix is simple:
change line 280: void sock_close ( int sock ); to static void sock_close ( int sock );
Note: this applies to sphinx 0.9.9, the last “stable” release at the time of this writing.