iperf 2.0 config problem

[Stephen Hemminger <shemminger --at-- osdl.org>]

For some reason the iperf-2.0 configure isn't picking up that
Linux (Suse 9.1) supports pthreads.

The following doesn't work correctly (in configure.ac)
but I am not enough of a autoconf expert to fix...
--------------

dnl check for -lpthread

if test "$enable_threads" != no; then
  ACX_PTHREAD()
    if test "$acx_pthread_ok" = yes; then
      AC_DEFINE([HAVE_POSIX_THREAD], 1,)
      AC_DEFINE([_REENTRANT], 1,)
    fi
fi