Help with audio/mangler and gsm

[Janik Galasso]

Hi eveyrone,

I recently ported audio/mangler but it was with out the gsm codec
because at this time  did not have the knowledge nor the time to try to
figure out how to make it work.

So recently I've looked at some of the ports I installed on my machine
and realized that multimedia/ffmpeg has it working. 

Here's the error I get when trying to configure it with the gsm codec
(which was installed when I activated it in multimedia/ffmpeg)

checking for gsm_create in -lgsm... no
Error: cannot find libgsm: Is it installed? Also make sure you have the
       libgsm development packages installed.
exit: Illegal number: -1
===>  Script "configure" failed unexpectedly.
Please report the problem to janik at hikarihq.com [maintainer] and attach
the
"/usr/ports/audio/mangler/work/mangler-1.2.1/config.log" including the
output
of the failure of your make command. Also, it might be a good idea to
provide
an overview of all packages installed on your system (e.g. an `ls
/var/db/pkg`).
*** Error code 1

Stop in /usr/ports/audio/mangler.
*** Error code 1

So I was wondering, does anyone have an idea on how to make see the
installed GSM?

Thanks
Janik